It is rather difficult to deduce the reason behind this behavior without being able to inspect the actual code. It seems that for some reason the AJAX request does not go well and after that the RadAjaxManager is missing from the page. Can you confirm it is not inside one of its update panels, as it shoud not be? Also, you are opening a new RadWindow from the RadWindowManager with and ID EditCourse, while the modal RadWindow you have separately declared has the AddCourse ID. This is located in the grdCourses_OnRowDblClick function. This is the reason why it is not modal.
Now, back to the AJAX issue, do you have the AjaxControlToolkit assembly in your project? We are aware of some cases where the MS AJAX scripts are referenced from this assembly instead of the original MS assemblies, and the version of the scripts that comes from ACT's dll is modified and does not work properly. If you have this assembly - please remove it from the project (entirely, it does not suffice to only remove references) and see if the issue persists.
If you are still having difficulties please isolate this issue in a simple, runnable project (no actual business logic, layout or dtasources are needed, just the bare minimum that shows the behavior you are experiencing) and send it back to us so we can examine it. You may find useful this blog post
on isolating the sample.
the Telerik team
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