The biggest upheaval was when the founder sold the forum without telling anyone he intended to do it. Most of the moderators resigned in protest and left the forum to set up their own, and many other members left as well. This is what kribensis12 is referring to. The protest forum has since ceased to exist.
The forum has been sold again since then and a lot of the problems associated with the first sale have been resolved. The main complaint was that the previously ad free site suddenly became inundated with ads after the sale. That was resolved shortly afterwards by having ads when not logged in, but the ads disappeared when logged in. Since then the ads have reappeared whether logged in or not, but not in such great numbers.