While realizing the backup of my googlemails I saw the following error message very often:

Error: Error while saving e-mail
Ignoring this error message.
If you want, please report the following traceback at www.gmail-backup.com/forum
Thanks! (gmb.py revision 691):
Traceback (most recent call last):
File "gmb.pyo", line 1225, in backup
File "gmb.pyo", line 956, in store
IOError: [Errno 2] No such file or directory: (always followed by a very long directory + filename...)

It is caused by an overflow of more than 255 characters composed by directory and filename e.g. of nearly all ebay emails. Nevertheless these emails are accepted and backed.

It would be better to give only a message, that the considered email name has more than 255 characters.