You need to get the script to display the name of the file that it 
failed on (unless you simply didn't show it in your excerpt) and then 
look at the permissions for the file in question.

Also it would be a good idea to catch the exception in your code so that 
you can report the error and then carry on. Also make sure that you do 
not process the any files that you have already processed on a previous 
run by ignoring file names that end in ".eps".