If you get FormBuilder, which has replaced validation toolkit, it will use the form name instead of the form array index.
What version of validation toolkit do you have instaled?
does it say: form
it may work if you update it to forms as well. Since it is the first (and only) form on the page, either syntax should actually work.
I'd make sure you have the most recent version of the extension installed, and if you do I guess it could be a bug that we would have to look into and fix.