I'm assuming this is the plugin you're using?
http://bassistance.de/jquery-plugins/jquery-plugin-validation/
From the site:
Please post questions to the jQuery discussion list, putting
“(validate)” into the subject of your post, making it easier to spot
it and respond quickly. Keep your question short and succinct and
provide code when possible; a testpage makes it much more likely that
you get an useful answer in no time.
And it goes ditto - if you have a test page, it'd be easier to take a
guess.
What exactly returns the HTMLObjectInputElement?
Have you tried throwing console.log() and see what Firebug shows?
-kb