Over two hours online today. This is really strange. less than 1 second after ACP calls the Talon6 roof controller with a CloseShutter() call, ACP silently exits. No popups, no "this program has stopped working" or "not responding" ... nothing. After some "zeroing in" on the problem, I put MessageBox calls immediately before and immediately after the call to CloseShutter(). The first one appears, clicking OK causes the shutter to start closing, then the MessageBox immediately afterward appears very briefly then the entire program simply disappears. No opportunity to click the OK in that second Message box. Poof!

I looked at the Windows Application log and found some weird stuff but it turned out to be unrelated. I interposed the ASCOM Device Hub between Talon6 and ACP. Same problem. Now for the capper: Saulius found that using the Close button in the Talon driver also causes ACP to exit!!

I'm totally baffled. At this point we're going to sit on it and see if some inspiration appears.