Well I have two problems:

1. the id you gave us is private so I can't get the page without a MySpace logon
2. When I use it on a non-private URL, it dies with a very helpful error message saying that there's no field called __EVENTTARGET.

So, what did it do for you?

Edited because there is a hidden field with that name. I guess that's the problem.

I don't set form fields that way, I just do

$mech->field( 'name', 'value' );
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and it seems to work.