Based on the article bellow if you set:
- Disabled - ScriptManager does not include any scripts by default and does not assume Microsoft Ajax will be used
- Explicit - you need to pick and choose and include the scripts manually based on what parts of the framework you need
- Enabled - the default, and the same behavior as before
In your case you are setting Explicit mode which does not include the necessary scripts, which RadControls for ASP.NET AJAX require.
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