How to close Modal Popup Extender
from server side code on click on close link inside the popup?
there is a property in extender for closing popup " CancelControlID" give button id in it and popup will close,if you want to close popup from server side mean from code behind then there is extender property hide(),in button code behind body write id of popup and enter "." after that you get all properties of popup in those property you get hide property.use it hopefully you will get the solution
example
private void btnSubmit_Click(object sender, EventArgs e)
{
modelpopupextender.hide();
}