Add the following lines on .aspx page

Text="Process" />


Add the following line on .aspx.cs page (Page_Load).

string strProcessScript = "this.value='Processing...';this.disabled=true;";
btnProcess.Attributes.Add("onclick", strProcessScript + ClientScript.GetPostBackEventReference(btnProcess, "").ToString());


This will disable Button, and then change the text of the button "Processing...", and then continue on with the server side event btnProcess_OnClick event handler.

Read more: http://feeds.dzone.com/~r/dzone/snippets/~3/1S6EfJZ3RWQ/14181