[eluser]BrianDHall[/eluser]
Wow, I'm stumped. It seems it must be your installation somehow. I would recommend creating a temporary fresh install of CodeIgniter 1.7.2 (the new version) and try this uploading on that fresh install with just your upload code and updated mimes.php and see what happens. Nothing is wrong with the code, so that just can't be the cause of the problem.