fckeditor in asp.net c# give error - XML request error: Internal Server Error (500)

Hi ,
         I am using fck editor in asp.net and c# .It works well on my localhost but it gives error on live server when i upload an image through fck,The error is

The server didn't send back a proper XML response. Please contact your system administrator.

XML request error: Internal Server Error (500).
Please help me some body.How  i can solve this issue.
Thanks,
VD

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