a python error normally gives the line number of the errors.  I dont see anything very obvious in the script, I dont like the suffix = " bit I prefer suffix = "" for a null string.

I would check that there are no stray characters at the end of the script and put in a few print statements to check the suffix value. any string containing a   will treat it as an escape character so if you have a X in any of your names that may be an issue.

suffix = Filename[13:] should get you the string, I dont think you need the len() part.