Well, I also stumbled upon this behaviour in my “early MOS days” - I simply forgot, that, if I started the “mos ui” which opens a window in a browser, the program won’t stop when closing this browser window. So when I switched to the CLI after closing the brwoser, the “Access denied” message came up when trying to access the device. After I realized that the MOS tool now was running with two instances, it was clear, that the first one with the ui blocked the port. So this is no error at all, but a question of awareness (at least in my situation), that MOS tool is already running.