Could not find a part of the path on windows azure

I deployed mvc-3 application on windows azure. In my application i am uploading the file an save it in the App_Data/DownloadedTemplates folder.

  var path = Server.MapPath("~App_Data/DownloadedTemplates");

my application is running on staging environment currently. When i uploaded file , it shows me an exception in the browser :

Could not find a part of the path 'F:\sitesroot\0\App_Data\DownloadedTemplates\B.htm_2c77cdfd-c597-4234-bd1e-29ca0a9b8d0e.htm'.

I am using Server.MapPath to locate the path of App_Data on the server, now why this exception ?. Can anybody tell me the problem ?