asp.net update panel validation

Question

I'm using an update panel in asp where i want to validate using the javascript. In that panel i have an dropdown,and 2 text boxes. The 3 fields are fetched from the database. in this case the dropdown has to be selected there. the dropdown contains account no from that any one should be selected. when i try to validate that using javascript it shows the alert msg and instead of validating it just saved the form. this all happens only when the panel is clossed and not when open.

any solution given it will be appreciated