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I have my PhD deadline on Monday and disaster has struck at the very last minute! Any assistance would be eternally appreciated.

I'm using Overleaf (v2) to write my thesis - it's a very large file tree containing multiple .tex files.

Everything was compiling fine, until I decided to experiment and use:


It compiled with this included but looked odd, so I deleted the line again. However, now it does not compile - despite the document being exactly the same as before the problem began.

marked as duplicate by user170109, Raaja, Mensch, siracusa, Sebastiano May 30 at 19:25

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    Don't know overleaf, but in other latex environments it can change things if you delete the *.aux file and possibly other files that were generated during compilation – sheß Mar 16 at 5:45
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    this is a question best answered by the CS of overleaf. They are very quick to respond. Please contact them. – Raaja Mar 16 at 6:19

If you changed your bibliography package from a BibTeX-based solution to biblatex or vice versa it is not at all unlikely that there would be some errors due to left over auxiliary files. BibTeX and Biber use these files to communicate with LaTeX (see Question mark or bold citation key instead of citation number for a great explanation), but the format of that file and its precise usage differs between biblatex and standard BibTeX. If the .bbl was produced for one method it will not be usable for the other. Usually latexmk (the tool Overleaf uses to compile your TeX document automatically) is quite good at sorting out issues like this, but sometimes it gets stuck with old file versions. In that case it helps to clear the auxiliary files (Overleaf calls this 'clearing the cache').

It is generally safe to delete the temporary files and recompile from scratch. Note that this answer also applies to a more general situation that does not involve switching between biblatex and BibTeX, but where the issue simply is caused by bad auxiliary files.

You can clear the auxiliary files via the following steps.

Click on the 'Logs and output files' button next to the Recompile button on the top of the rightmost pane, it will probably show the number of errors in a red box (highlighted in light pink in the screenshot).

The 'Logs and output files' button

You will be greeted with a digest of all error messages and warnings that LaTeX and other auxiliary programs like BibTeX or Biber reported. Scroll down to the bottom of the page. On the bottom right you'll see a little dustbin icon (highlighted in blue). Its hover-text says 'Clear cached files'. That button allows you to get rid of all temporary auxiliary files (.aux, .bbl, .bcf, ...).

Dustbin icon

A popup messages asks you to confirm.

Confirm dialogue

If you press "Clear cache" in that window, Overleaf deletes all your temporary files. You can then recompile and the error should be gone.

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