Note that it is quite likely that this is caused by a specific homework set in a particular class, and most likely a particular problem in that set.
Also, for those viewing this in the future, note that Danny's information about where the temporary files are stored is valid for WeBWorK 2.16 and before. As of WeBWorK 2.17 those files will be stored in /opt/webwork/webwork2/tmp/[coursename]/hardcopy. Furthermore, those files will not be publicly accessible. Only the user that generated the files will have access to them from the web.