I already answered the support ticket on the subject. For convenience I will paste my answer here as well.
RadFileExplorer heavily relies on ASP.NET client callbacks, which do not work very good with the MS Ajax framework and ajaxifying the control should be avoided.
However, to be able to provide more to the point answer we will need to examine the exact page setup to suggest the best practice for it. Could you please provide fully runnable sample project demonstrating the problem?
the Telerik team
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