This error comes because WWW::Mechanize does not find a field by that name in the current form. Maybe such a field does not exist.

Inspect your current HTML and your current form and look if they are what you think they are. Convenient methods for inspecting are:

print $mech->content;

$mech->save_content('progress.html');
[download]

Also, the documentation recommends the mech-dump utility for inspecting a page and its forms and fields.

Have you looked at WWW::Myspace ?