Hi Rajiv,

You can custom the file too large error message by property "FileTooLargeMsg", like below. So you can shows your own message.

      <CuteWebUI:UploadAttachments ID="uploader1" runat="server"  FileTooLargeMsg="custom error message">
            <ValidateOption MaxSizeKB="1024" />
        </CuteWebUI:UploadAttachments>
 

Regards,

Ken