So for future reference: this particular problem (involving errors while creating images of equations) was debugged by setting
$WeBWorK::PG::ImageGenerator::PreserveTempFiles = 1;
$WeBWorK::ContentGenerator::Hardcopy::PreserveTempFiles = 1;
The two variables do similar things. Normally when TeX is run there are a number of auxiliary files that are created during typesetting and these are cleaned up after the job is done. Setting the PreserveTempFiles flag to 1 inhibits the clean up of these temporary files so that you can manually inspect the files, try to run various portions of the typesetting process and determine exactly where the problem is occuring.
The Hardcopy::PreserveTempFiles flag governs the creation of hardcopy output of homework sets. The ImageGenerator::PreserveTempFiles flag governs the typesetting of equations for the image mode of presenting mathematics on the screen.
The thread at
incorrectly references the Hardcopy::PreserveTempFiles when it should have
referred to the ImageGenerator::PreserveTempFiles flag for the problem at hand.
Thanks for Jay for helping to make clear how to trouble shoot this problem.