WP at least with it reporting as an "internal server error" you know it is the forum hoster at fault and not any network, routing or DNS issue, these usually come up as "Page cannot be displayed" or "Server not found". I have to admit that this forum is one of the more unstable ones I have been involved with but I know its not your fault. From my previous experience as a forum admin,
http://www.freeforums.org is one of the most reliable out there. I ran a forum on there for over 3 years and in that time only had one unscheduled outage and about 4 scheduled outages and one of them was to switch from phpbb2 to bb3. If your current hoster give you the runaround and the instability issues continue, I'd suggest you go take a look at their services. Whilst they host free forums, they have premium forum packages which offer all the extra trimmings like attaching a website portal as you do now.
Let me state that I have no affiliation with freeforums, I've just used them in the past and they were great.