First off, you want to "Rebuild Article List." Not "Rebuild Link Cache." This is simply to repair any damage that the rename operation may have caused. Also if you are receiving that other error I think you are still running RC3 and not the stable version.
You will not be able to (safely) rename any forum marked as wiki until the next build, but I think the new title would still be saved even though you received the fatal error (in this case, it may be necessary to "Rebuild Forum Counters" for the changes to take effect).