I can't get the door to Suran Guardhouse to work. In-game it just says "door" and rotates 90 degrees when activated. I can leave the guardhouse just fine but can't enter it. I've checked in the construction set and the doormarker does say it's meant to go into the suran guardhouse interior. The doormarker itself was pointing diagonally from the door instead of straight out but rotating and moving the arrow so it is placed in the same way as other doormarkers has had no effect.

I had Suran Underground installed but this only adds a trapdoor inside the guardhouse and I have used the mod without these problems for years. Also, I have tried a fresh install with just MGSO and that didn't work either.

I haven't played Morrowind in years before this and have barely touched the construction set anyway. Is there some part of the process of mending the door that I'm missing?

whats it say under teleport when you double click the door in the CS

Its a known issue of MGSO. Get the patch for that and many other problems from the http://www.gamesas.com/topic/1513057-relz-morrowind-overhaul-sounds-graphics-30-thread-6/.