Did you intentionally omit the (optional) 'button' argument to submit_form? Why the comma character after \%fields? It seems to me that the interpreter is complaining about your failure to call submit_form in a recognizable way.

Update: Yeah, sorry, that was nonsense -- a quick sample script works fine with or without the comma after \%fields. (Blush).

Have you tried using Data::Dumper to look at the contents of $mech before you attempt the submit_form? I'm getting decent error messages in my sample attempt with screwed up arguments (no form by that number exists, no field by that name exists, etc.). What version of WWW::Mechanize are you using? Line 1492 on the most recent version is in the middle of some POD ...