I've found out a bit more... Websense is now starting to categorize all forum-type sites as "social media", and any user that chooses to have Websense block social media will block it. However, I notice that several other forums that I participate in are not blocked. As near as I can tell, the difference is that those sites do not have the forum index at the home-page level; you have to select "forum" on the home page to go to the forum, and apparently Websense's software does not pick that up. I'm not at all sure what to do about it... we aren't Facebook here!
Bit ominent isn't it... I mean we don't know what we are being blocked from seeing - there is no way to tell...