Sometimes cryptic errors occur if there was a syntax error in a .bib BibTeX bibliography file that doesn’t disappear even when the .bib syntax is corrected. The fix for this is often to delete the auto-generated files:

• .bbl file.
• .aux file

Example: top-level LaTeX file “main.tex”. The compilation generates main.bbl and main.aux among several others. Try:

rm main.aux main.bbl

pdflatex main
bibtex main
pdflatex main
pdflatex main