Scratch that, still lots of problems, even though I fixed the issue above. Not sure what's up but a lot of people can't post, edit or upload images.

Ok, I've narrowed it down to a conflict with the SureMembers plugin. I'm not sure if the problem is on wpForo's side or SureMembers side, but wpForo was recently updated in a huge way and SureMembers is a new plugin on the scene.

Disabling SureMembers allows wpForo to work properly again. While activated, SureMembers seems to work properly without error.