It appears your server doesn't have a temporary folder set to an existing folder or the folder doesn't have the correct permissions.
I set up a simple file upload page to help demonstrate the problem:
You will see it gives Error->6
That error is:
Value: 6; Missing a temporary folder. Introduced in PHP 5.0.3.
Ask your hosting provider to look into the php.in value for upload_tmp_dir and make sure it is set correctly and that the folder specified has the correct permissions.