Look at your <form> tag where the file is uploaded...
does it have:
<form enctype="multipart/form-data" method="post" >
That is what I mean by that part. The server behavior is the Universal Email interface where you set all of the universal email settings.
The other settings that could be wrong are in the php.ini file.
If you want to set up a time for an engineer to call you, you would have to purchase a premium support ticket. However you can continue to post questions here and I'll try to help as best as I can.
If you wan to attach a zipped copy of the page that you are submitting and the include file for the email I can take a look and see if those are the problem. If not it is most likely the upload_tmp_dir in your php.ini file and I can give you a script to test that as well through this forum.