The issue you experienced is a feature of ASP.NET - deleting a sub-folder in the application directory will trigger a restart of the web application. If your session is stored in the application memory, it will be erased. This is not connected with the RadFileExplorer control - the same behavior will occur if you delete the folder from windows explorer. Here are some useful links on the matter:
One possible solution we can recommend is to move your session data to a state server or a SQL server. This way it will not be lost when the AppDomain is restarted.
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