I have sometimes had a similar perl error mesage when running some scripts which read XML files and parse them. The problem is quite likely to be in your data or more specifically in the fact the data isn't matching what the script is expecting to handle.

I usually found that my script was trying to use a variable which had not been set a value. I would suggest finding what line 427 of CSV.pm is trying to do and see why you would have an undefined variable.