A station can only have the state blocked if it contains an MU and that MU can't move forward. However if you only want to prevent MUs from entering a station the solution is simple.
Say that you want to block stationY when stationX is working: On the entry control for stationX you write:
StationY.EntranceLocked := True StationY.ExitLocked := True
And on the exit control on stationX you write
StationY.EntranceLocked := False StationY.ExitLocked := False
However, if a part is on stationY when a part enters stationX, it won't be able to leave until stationX is finished. This can be fixed by simply omitting the "stationY.exitLocked" command.
For the exit control you also have to add the command "@.move". I forgot about that, sorry. So the code should be:
Station5.EntranceLocked := False Station5.ExitLocked := False @.move
Also you should create an init method to unlock your stations at the beggining of the each run. (Add a method object and rename it to "init")
Station5.EntranceLocked := False Station5.ExitLocked := False