I was working with phpMyAdmin and I got the following error:

 File upload error - unable to create a temporary file in Unknown on line 0

The problem was that the upload_tmp_dir setting in my php.ini file was specified twice. Once up the top of the file where I was editing it, and then later in the file where I didn’t see it. So the setting I wanted wasn’t being applied. If you get this error double check you’ve only got one setting for upload_tmp_dir.