Gilden got wiped out by either Magnar or Monsters dont' remember. But I found this outpost of his in a prime spot. Went to build there and even though hes dead, its stopping me from building there. Also since I can't declare war against a dead player I can't destroy the outpost.
Heres a screenie:
I can provide a save file if you need it too if this isn't a commonly ran into issue.