A couple people have reported that the standard combination doesn't work for them, or that they played around with the levers and got another combination to work. Leaving the SW and NE levers up and pulling the NW and SE levers down should open all 4 doors to the small rooms. Perhaps the game sometimes gets confused about a lever's position, or the levers do not get reset properly exiting the house, or something. In any case, once the 4 doors are open you should just have to pull the central lever down to close them and open the treasure room door.
Did you put all the levers in the up position, then leave the house (and maybe even Verdistis) to see if that would reset the levers and get the combination to work? You shouldn't have to put the levers up yourself, but it wouldn't hurt to try it.
There can sometimes be a gap in the north west corner when two walls meet, which it may be possible to toss a teleporter stone through. You could check that corner of the treasure room in Sir Patrick's house, and see if you can see into the house from the outside, and drag and drop a teleporter in.
You could use the file swap procedure described in the
FIX for the Missing Catacombs Portal topic to get into the locked room, but I would have to find one of my old saves at that point to get a suitable data file.
Another possible way into the room;
Teleporting Anywhere, via hex editor 
