It is possible that you forgot to add the attached file in the attachment section of the UE Server Behavior? Maybe referenced it wrong there?
If you have added it to the attachments section properly, it could be that your form is not using the POST method, or enctype isn't set to "multipart/form-data".
Another possibility is that the file you attached is too large to be uploaded, or that the upload_tmp_dir in your php.ini file is set to a directory that doesn't exist or doesn't have adequate permissions.
Did this help? Tips are appreciated...
