Hope you've sorted this out by now but I had the same problem, trying for 45 minutes. Once I'd walked away and calmed down, I worked it out.
The front of the filter turns independently of the rest of the filter, so it creates a seal by squeezing the rubber seal against the walls of the hole.
The problem for me was that the screw mechanism was over wound to its tightest point so it wasn't moving independently of the rest of the filter. When I was replacing it, I thought that the whole thing was supposed to turn in the hole and couldn't make this happen so was getting incredibly frustrated.
What I had to do was to undo the front part of the filter - i.e. unscrew the front part of the filter by holding the filter part steady and turning the front part anti-clockwise. The whole thing came apart in 3 pieces.
It becomes obvious at this point but I then reassembled it so that the rubber seal was no longer squeezed out, replaced the filter and screwed it in.
Ta da!
TH, December 2009
