This type of Page is not served

Hello Everyone,
  I am using WYSIWYG editor. When i click on File Upload(in WYSIWYG) to upload  a file, a window to enter File details opens up. But when i click on Folder to upload image, error comes 'This type of Page is not served' & in Requested URL it displays /<ProjectName>/assertManager/assertManager.asp. Mine is an .aspx application(C#) but for Content Management this .asp application is used.
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