How to Prevent Double click in Asp.net
The following snippets will prevent you from the Double click 
 Just use the below line code under page_load event:
 | cmdSubmit.Attributes.Add("onclick", "this.disabled=true;" + ClientScript.GetPostBackEventReference(cmdSubmit,"").ToString());note:-  cmdSubmit should be Asp.net Button Name | 
for more information visit the site:
http://shawpnendu.blogspot.in/2010/02/how-to-disable-multiple-button-click-in.html