Explain my error

When you need this page: When stuck

Paste the error, or the whole log, from Overleaf or your editor; the page finds the first real error and says what it means and how to fix it. With a whole log, it also lists the other errors and the warnings worth a look.

Nothing is uploaded. The page reads the text or the file in your browser and saves nothing. Still, remove anything confidential before you paste it anywhere.

The explainer needs JavaScript, which is off or not available in this browser. Look for your message under Show all the messages it knows, or read the error yourself with Read an error message.

Where to copy the error from

Overleaf: click Logs and output files beside Recompile. Copy the first error, or open Raw logs at the bottom of the list and copy all of it.
VS Code: open the Output panel and choose LaTeX Compiler, then copy all of it. View → Problems lists the errors too.
Another editor: copy from its log or messages panel, or choose main.log (in build/ or next to main.tex) with Choose the .log file.
The optional build helper: copy what it printed after First error.

Fix the first error and compile again, since the later ones are often side effects. The page marks the part of the l. line that LaTeX read before it stopped, and says where to find the file and line in VS Code and on Overleaf. If the page does not know the message, it shows the steps from Read an error message.

Under the first error, a closed list (Also in the log) counts the rest: other errors, citations and references not found (with their names), lines too wide or loosely spaced (with the file and lines), missing characters, and notes such as Biber has not run. Each says what it means and links to its fix. After a first compile, citations and references are often listed only because the bibliography step has not run yet: compile again before you look for typos.

Messages this page knows

The same table is used by the optional build helper and by common messages, so all three give the same advice. Common messages also covers problems that show no message, such as a figure that moves to another page.

Show all the messages it knows

What you see	What it means and what to try
File `rpi-thesis.cls' not found	LaTeX cannot find the class file, so it is not compiling the starter's folder. Extract the whole ZIP and open the folder that contains `main.tex`. In an editor on your computer: Open the folder itself (File, Open Folder in VS Code), not only `main.tex`. On Overleaf: `main.tex` and `rpi-thesis.cls` must be at the top of the file list, not inside a folder. More: Common messages, Setup and files.
`Missing title in metadata.tex (or author, department, ...)`	A required setting in `metadata.tex` is empty or missing. Fill in that setting inside `\thesissetup{...}` in `metadata.tex`, then compile again. More: All thesis settings.
`Committee chair is missing`	No `\committeemember` line in `metadata.tex` has the role `[Chair]` or `[Co-Chair]`, spelled exactly so. Put `[Chair]` (or `[Co-Chair]`) on one `\committeemember` line: `[chair]` is not recognized. More: All thesis settings.
`You have requested ... version ... of document class rpi-thesis`	Your `rpi-thesis.cls` is older than the rest of your starter files. Copy `rpi-thesis.cls` from the newest starter into your thesis folder, replacing the old one. More: Update the formatting safely.
`Unknown setting "..." in metadata.tex`	A setting name inside `\thesissetup{...}` is misspelled or does not exist. Correct its spelling; every setting is listed in All thesis settings. More: All thesis settings.
`Unknown degree choice`	The degree setting in `metadata.tex` has a value the class does not know. Use masters, doctoral, or engineering-doctorate, in lower case. More: All thesis settings.
`Unknown graduation month`	The graduation-month setting in `metadata.tex` has a value the class does not know. Use May, August, or December, with a capital first letter. More: All thesis settings.
`Graduation year must have four digits`	The graduation-year setting in `metadata.tex` is not a four-digit year. Write the year like 2027. More: All thesis settings.
`RPI seal not found`, or a seal placeholder on the title page	The seal belongs to RPI, so the starter does not include it; the title page keeps a box of the same size in its place. Download the seal from RPI's Thesis Preparation page and save it as `assets/rpi-seal.jpg`, then compile again. On Overleaf: Upload the seal into the assets folder in the file list. More: Add the RPI seal.
`Unsupported class option`	`main.tex` gives the class an option in square brackets, such as [11pt]; this class takes none. Use `\documentclass{rpi-thesis}` with no options; settings go in `metadata.tex`. More: All thesis settings.
LaTeX Error: File `figures/...' not found	A figure file named in `\includegraphics` is missing. Check the file name, capital letters, extension, and folder (`figures/...`). In an editor on your computer: Compare the name in `\includegraphics` with the file in the figures folder. On Overleaf: Upload the picture into the figures folder in the file list, then compare its name with the one in `\includegraphics`. More: Common messages, Setup and files.
LaTeX Error: File `chapters/....tex' not found	A file named in `\include` or `\input` does not exist under that name. Check the file name and folder in the `\include` or `\input` line in `main.tex`: write it without .tex, with the same capital letters as the file. More: Common messages, Setup and files.
`Could not set up appendices`	A line above `\documentclass` in `main.tex`, or an outdated LaTeX installation, changed `\chapter`. Remove lines added above `\documentclass`, or update TeX Live. More: Common messages, Setup and files.
`Misplaced alignment tab character &`	An & is outside a table; most often a title in the .bib file contains &. Write it as `\&`. More: Common messages, Citations and references.
`Please (re)run Biber on the file`	The bibliography step has not run since your last change, so citations show as keys in bold. Compile again. In an editor on your computer: VS Code with the starter's settings runs Biber for you; in other editors run the bibliography step yourself (Get started, Other editors). On Overleaf: Recompile; Overleaf runs Biber for you. More: Other editors.
Citation `...' undefined, or Reference `...' undefined, or ?? or a bold citation key in the PDF	A citation or cross-reference is not known yet: it fills in on a later compile, or its key does not match. Compile again. Still there? Check that the key in `\parencite` or `\ref` matches `references.bib` or the `\label` exactly, then compile again. In an editor on your computer: VS Code with the starter's settings runs the bibliography step for you; in other editors run it yourself (Get started, Other editors). More: Bold citation keys and question marks.
`File 'main.bbl' not created by biblatex`	A bibliography file left from an earlier build, often one that used BibTeX or natbib, is still in the folder. Do a clean recompile, then build again. In an editor on your computer: In VS Code, run LaTeX Workshop: Clean up auxiliary files; with the build helper, python3 scripts/build.py --fresh. On Overleaf: Open the Recompile menu and choose Recompile from scratch. More: Clean recompile.
`Label(s) may have changed. Rerun to get cross-references right`	Numbers, references, or bookmarks changed in this run; the next compile settles them. Compile again. More: Common messages, Citations and references.
`Undefined control sequence`	LaTeX does not know a command, usually because of a typo after a backslash, such as `\parencit` for `\parencite`. Look at the end of the l. line: the last command there is the one LaTeX does not know. Correct its spelling, or load the package it comes from. More: Read an error message.
`Missing $ inserted`	A math-only character or command, often an underscore _ or ^, is outside $...$ . Write `\_` for an underscore in text, or put the math between $ signs. More: Common messages, Layout and the PDF.
`Runaway argument, or a brace error`	A { has no matching }, or there is one } too many. Check your last edit near the line shown for a missing or extra }. More: Common messages, Layout and the PDF.
`Environment ... undefined, or \begin{...} ended by \end{...}`	The name in `\begin{...}` is misspelled, its package is not loaded, or a `\begin{...}` and its `\end{...}` do not match. Check that each `\begin{name}` has an `\end{name}` with the same spelling, in the right order. More: Read an error message.
`Missing character: There is no ... in font ...`, or a special character (such as an accented letter, or one from another alphabet) is missing or garbled	The font or compile engine has no shape for that character. Use a LaTeX accent command, such as `\'e` for an e with an acute accent, or try another compile engine. More: Choose a compile engine.
`STIX Two Math font not found`	LuaLaTeX or XeLaTeX could not find a fallback math font, so a few symbols, such as `\bigstar`, `\digamma`, and `\subseteqq`, may be blank. Update your full LaTeX installation, do a clean recompile, then check the affected math. On Overleaf: Choose the newest TeX Live version in Overleaf's Settings, then do a clean recompile. More: Common messages, Layout and the PDF.
`Overfull \hbox`	Something is wider than the text area: a long URL, table, equation, or image. Find it in the PDF and resize or break it. More: Too wide for the page?.
`Overfull \vbox`	Something is taller than the page: on the title page, usually the title or a committee line; elsewhere, a large figure or table. On the title page, remove manual line breaks from the title and check long names and committee lines. Elsewhere, make the largest figure or table on that page smaller. More: Common messages, Layout and the PDF.
`Pre-submission hints (your PDF was built; check these before submitting)`	Your PDF was built. The build helper found things to check before you submit, such as a web source with no access date. Fix each listed line before submitting. More: Build commands.
`Unicode character ... not set up for use with LaTeX`	pdfLaTeX cannot print one character in your text, often a symbol or letter pasted from Word or the web. The message names it, and the l. line ends with it. Replace that character with a LaTeX command (for example $`\geq`$ for the greater-than-or-equal sign), or compile with LuaLaTeX and check the PDF: its font must have the character. More: Going further, Choose a compile engine.
`Underfull \hbox (badness ...)`	LaTeX stretched the spaces in a line or page, often after \\ or `\linebreak`. Usually harmless. Look at those lines in the PDF; remove a manual line break if the spacing looks wrong. More: Common messages, Layout and the PDF.
`latexmk, pdflatex, or biber not found, or spawn latexmk ENOENT`	A LaTeX tool (latexmk, the engine, or Biber, the bibliography tool) is not installed, or your editor started before the installation finished. Finish installing the full LaTeX distribution, then quit your editor completely and reopen it (on Windows, restart the computer if needed). In an editor on your computer: On Linux, use VS Code's .deb or .rpm, not the Flatpak. The optional build helper's setup check names the missing tool. On Overleaf: Overleaf has every tool; this message comes from a LaTeX installation on a computer. More: Common messages, Tools and installs.
LaTeX Error: File `....sty' not found	A package named in `\usepackage` is not installed, or its name is misspelled. Check the spelling in `\usepackage`; if it is right, install the full LaTeX distribution or update it. On Overleaf: Overleaf has nearly every package: check the spelling in `\usepackage`. More: Common messages, Tools and installs.
`latexmk: could not find the script engine 'perl'`	latexmk needs Perl, which MiKTeX does not include. Install TeX Live instead (https://tug.org/texlive/ (opens in a new tab)), or install Perl and restart. More: Common messages, Tools and installs.
`Package fontspec Error: The font "..." cannot be found`	LuaLaTeX or XeLaTeX cannot find a font: the LaTeX installation is not the full one, or a font name added in `preamble.tex` is misspelled. Install or update the full LaTeX distribution. If you named a font yourself, check its exact name, or remove that line to use the class's font. On Overleaf: Choose the newest TeX Live version in Overleaf's Settings, then recompile. More: Common messages, Tools and installs.
`You have requested release '...' of LaTeX`	Your LaTeX is older than this class needs (TeX Live 2022 or newer). Install the current full TeX Live (https://tug.org/texlive/ (opens in a new tab)), or use Overleaf. On Overleaf: Choose the newest TeX Live version in Overleaf's Settings, then recompile. More: Common messages, Rare messages.
`Found biblatex control file version ..., expected version ...`	This is most often a stale control file left by an earlier build. Do a clean recompile, then build again. If it still fails, Biber and biblatex come from different TeX installations or years: use one TeX distribution, update it completely, and make sure 'biber' is the one it installed. In an editor on your computer: In VS Code, run LaTeX Workshop: Clean up auxiliary files; with the build helper, python3 scripts/build.py --fresh. On Overleaf: Open the Recompile menu and choose Recompile from scratch. More: Clean recompile.
`biber ... lipo (on a Mac)`	Biber, the bibliography tool, could not start: older Mac builds of Biber fail on newer macOS. Your thesis is fine. Update TeX Live, then compile again. In an editor on your computer: On macOS (MacTeX), open TeX Live Utility (Applications, TeX) and choose Update all packages, or run 'sudo tlmgr update --self --all'. On Linux with apt, update with your package manager, for example 'sudo apt update' then 'sudo apt upgrade'. On Overleaf: Overleaf installs Biber for you; this message comes from a LaTeX installation on a computer. More: Common messages, Rare messages.
I can't write on file `chapters/...aux'	LaTeX cannot create a chapter's .aux file, because that chapter's folder does not exist where LaTeX writes its scratch files. Do a clean recompile. If you typed your own build command, use one from the build commands instead. More: Build commands.

Still stuck? Ask for help with the first error, its file, and its line number.

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