[jQuery] [validate] Issues in IE6

Hi,
I've got form validation using http://bassistance.de/jquery-plugins/jquery-plugin-validation/
working well in Firefox 2, Safari 3.1, Opera 9.5 etc but throwing up
an error in IE6.
I can't see what's wrong, any suggestions?
http://www.edenvillamedical.co.uk/
The form in question is under the 'Prescriptions' tab. 'Patient Name'
is required.
Appreciate any help.
Many thanks
Matt