Asp.net/SharePoint button Click event fires only once

Problem: Response.end and download file problem using asp.net code inside SharePoint. Button click event fires only once when it is first clicked. After that,button no longer respond to click event.

Solution: Insert below script block.
function enablePostBack()
{ window.WebForm_OnSubmit = function () { return true; }; }

button.Onclientclick="enablePostBack";