I was able to cure what was breaking in the forum by upgrading to the latest version of the software. At least, it's cured as far as I can tell, so I've brought it back online.
The hosting company is still working on the server. Something may break again with no warning, especially since I've made substantial changes to the site compared to what is in their backup. At least I won't have to go through several dozen manual database changes again. The automated database update choked on our 220K posts. :D