Hi Dude

I hope it helps but i think that this is a Jquery Clash thinky which means you either enabled a recent module that loads Jquery after it has already been called by Virtuemart.
I suggest starting with the obvious and disallowing all modules that you can to find the conflict, if that doesn't help i will need to know more details about your configurations such as what virtuemart version are you using(2) if so did you update it recently? ... well hope you solve it quickly.
P.S
I noticed your site YCC has been hacked

if you need secure hosting i can help with that too
