Scripts

function GarrisonBlock()
  while 1 do
    if GetObjectOwner("Fortress_2")==GetObjectOwner("Dungeon_1")  then
      SetObjectEnabled("Garnizon_1", 1, GetObjectOwner("Dungeon_1"))
      while not IsObjectEnabled("Garnizon_1") do sleep(1) end
    end
    for i=1,8 do
      if GetPlayerState(i)==PLAYER_ACTIVE and  i~=GetObjectOwner("Dungeon_1") and i~=GetObjectOwner("Fortress_2") and IsObjectEnabled("Garnizon_1") then
        SetObjectEnabled("Garnizon_1", nil, i)
      end;
    end;
  sleep(1)
  end;
end;

startThread(GarrisonBlock)

I put the second sleep(1) in the wrong place, so the loop was running without a pause, and the game would freeze if the condition wasn't met.