Can't, like it won't let you (a bug), or don't know where it is? The housing zones are off of the Guild Lobby. If you're looking at the Magus, and the two guild hall doors, the neighborhood zone line is to the left, through the room with the bulletin boards.
It sounds to me like what happens when the zone is down. Perhaps try a different neighborhood. Also, are you choosing a guild neighborhood, for a guild you are not in? I don't know, but can a guild configure it so ONLY their guild members can enter a guild neighborhood? Ooohh, also. What server are you on? If it's a TLP which is at an expansion before housing was introduced, that's the most likely culprit.
DB screwed the pooch .. the guild Neighborhoods are bugged .. or down ..(at least our guild) every time i tried to zone into the GGH left door .. it zoned me into the basic GH (right side) my guild leader said they are working on the issue and have a ticket in with DB .. I even went to the guild neighborhood via the zone and went to Guild plot and tried to zone in with the actual front door of the guild hall did not work just zoned me into the basic GH again .. sounds like this might be OP issue ??