HI rathiDigimagic,
Do you get this error with speical file/size/extension? Or it is a randomly problem?
Please set UploadType to iframe and set UploaderDebug to 1 then try again. what error message you get form the debug window?
<CuteWebUI:UploadAttachments ID="uploader1" runat="server" UploadType="iframe" UploaderDebug="1">
</CuteWebUI:UploadAttachments>
Is your site online? if so, can you post your uploader page url? So we can check it for you directly.
Regards,
Ken