Appointments+ and/or WPMU Dev Dashboard are breaking the site (whitescreen/500 error)

I came in this morning to frantic calls from a client that his website was missing… WordPress admin and all. Managed to track it to a plugin issue, deactivate them all through phpMyAdmin, and reactivate them one by one, which narrowed it down to Appointments+ and/or WPMU Dev Dashboard. I tried updating them, but that didn’t seem to help. I tried updating WordPress, no joy there either. So, the site’s back up, but I have to leave your plugin(s) deactivated to keep it that way, which kinda sucks since I’m paying for it! Help!