Thought I would put this here in case others experience the same thing.
Although having previously successfully entered a Hak area, when trying to yesterday I kept crashing and then could not log in with that PC.
It seems that occasionally your Haks can get 'switched off'.
So I had to log on with a different PC on that login account and use the "/c haks on" command.
When I then relogged in with the PC that was trying to enter the Hak area, it worked fine.