Only one instance of a ScriptManager can be added to the page in asp.net C#
Solution :
It says it right there...when you have added the Script Manager in page as well master page, you have to use only One Script manager.
Master page and current page both contains scriptmanager. Remove extra script managers and there should only be one script manager object on one page and child pages.
We can use one script manager on a single page only. If we want to utilize script manager at master page then use proxy script manager at master page, this will make you to not mention script manager at each page. As per my concern you can use a single script manager on one page not multiple. Within which you can use ur content, update panel etc Ajax tools.
