<b><big>The control with ID 'ControlID' requires a ScriptManager on the page. The ScriptManager must appear before any controls that need it.</big></b>
Seems like you are trying to use any of the AJAX based control on your webpage. In order to use them, you need to put 'ScriptManager' control your webpage - it handles the AJAX based scripts and workflow.
From your toolbox, drag drop a script manager on the webpage at the of page design.
somewhere on your web page you have used ajax control. So in your page where ever you have placed that ajax control just put Script Manager control anywhere above that ajax control in that page.
Script manager is ajax Control and will not get displayed on run time.
It basically contains the parent classes which underlying ajax controls will use.
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