stop firing textchanged event of a textbox when autopostback is true and a validation error araises in ajax

hi..

i hv one textbox which has autopostback="true" and it is associated with a regular expression validator. so my problem is when a validation error occurs the page is postback and textchanged event is fired which should not be ...

so what is the solution to stop textchanged event handing...

any suggestion will really appreciable..

thanks