Allen:

 

You can use the OnFileValidating event to write the custom validation code :

 

<CuteWebUI:UploadAttachments runat="server" ID="Uploader1" OnFileValidating="Uploader1_FileValidating" />

 protected void Uploader1_FileValidating(object sender, UploaderEventArgs args)
 {

      if(!CheckFileStream(args.OpenStream()))

            throw(new Exception("You file is not valid!"));

 }

 

this exception message would pass to client side , and the uploader would alert it to the users.

 

Regards,

Terry