I couldn’t open auxilliary file

Arrrgh.

I just spent 90 minutes tracking down a bug in my LaTeX code. It kept failing with “i couldn’t open auxilliary file filename.aux”.

What was actually happening was that I’d mistyped the name of an included image in my chapter3.tex file and rather than failing with some sort of intelligent message like “there’s no image by name imagename” it was merrily going along and failing in a totally undefined way. Excellent. Of course, the debug message was such that it seemed like the error was in the subsequent file, chapter4.tex because it seemed that the system was saying that everything was cool in chapter3.

This post made in the hope that someone, somewhere comes across a similar problem, googles for it and finds this page.
LaTeX: Beautiful output; not user friendly.