Problem with compiling BibTex: "no \citation commands" error

I noticed this problem when I used biblatex without having specified the backend=bibtex package option. Adding the option fixed it.

I'm a TeXstudio user and whenever I receive this error message, it's because I've changed the default bibliography tool from biber to bibtex.

To change it back, I have to do Options > Configure TeXstudio > Build > Default Bibliography Tool and the process works again.

Even if this answer never helps anyone else ever, it'll at least be good for me to have this here as a aide memoire next times this happens!

As explained on the second page of the BIBTeX manual the new command \nocite{*} allows, since version 0.99b, to

include in the reference list every entry in the database files, without having to explicitly \cite or \nocite each entry. Giving this command, in essence, \nocites all the enties in the database, in database order, at the very spot in your document where you give the command.

This is useful since BIBTeX, by default, do not consider uncited entries of the database. This behaviour can look strange but is the right way to proceed: if you don't cite anything, it means that you haven't used any information from the entries in the database in your document! So the best way to proceed is to find a place to cite every entry.