[jQuery] Help with ajaxForm in tabs, file uploads fail with strange error

[Giovanni Battista Lenoci]

Hi, I'm going crazy with file upload ans ajaxform when the file field
is in a tab.

When I click on submit button I got this error in firefox console:

form.submit is not a function
(?)()()jquery.form.js (riga 223)
[Break on this error] form.submit();

I've put a sample page here:

http://lab.gianiaz.com/jquery/file_upload_in_tab/index.php

Thank you in advance.