Bob, I admit to being even more lost after your answer. I agree that it is due to the fact that a "ShutterStatus=4" is returned. However, when you lool at the ASCOM logs, there is no error somewhere: how such an flag can be raised? Is-it really coming from the dome or is-there a trick somewhere (my question is probably, but there is something that really escapes me)? To be honest I am not (yet) convinced that it is coming from the controler: I really need more elements to discuss with Michael.

For the scheduler, I can let it manage the dome. But, when schools are observing, it is desactivated and we need something automatic to open the dome. I then used once of your script and slightly adapted it. If you have suggestions, they are more than welcome.