The RadUpload control does not work the same way as the standard ASP.NET FileUpload control. To read the uploaded file, it would look something like this:
// get uploaded file
UploadedFile attachment = upAttachment.UploadedFiles;
// create byte array
 attachmentBytes =
// read attachment into attachmentBytes
attachment.InputStream.Read(attachmentBytes, 0, attachmentBytes.Length);
I hope that helps.