Error - Exception thrown without a stack from in UNKOWN line 0

Exception thrown without a stack from in UNKOWN line 0

I get this error when I hover the mouse over a users profile thumbnail, after a few seconds the 'contact / block  / report 'buttons show up over that user, but this error is written underneath.

Any ideas whats causing this???

Never heard of this one before!

http://www.boonex.com/forums/?action=goto&search=1#topic/Fatal-error-Exception-thrown-without-a-stack-frame-in-.htm

Thanks Deano :-)