Drupal 6.13 upload http error 0

I have a custom version of Drupal 6.13 installed (not the one-click). The upload module is broken on my site (HTTP error 0). I’ve tried every suggestion from Drupal.org to fix it but nothing works. Then, when I saw the message in my status report about the PECL uploadprogress library, I thought it might be related. Unfortunately, to get the PECL uploadprogress library, I would have to install my own PHP5. Of course, that then makes me responsible for keeping it up to date, which I’m not keen on.

Has anyone else experienced this issue?