Necroing this topic. I'm having the same issue. Now, granted this isnt _too_ important to me because I'm trying to play from work at the moment, but let me explain how this all went for me:
Installed the game just fine, I dont have administrator credentials but for this it didnt matter. Game installed fresh and worked immediately no problem. Played through most of the Ruins-related government quests with my nephew, about 2-3 hours of uninterrupted gameplay.
Shift was nearing its end and I decided theres no time to do a full clear of Ruins to finish the story, especially since I am often pausing in corridors to handle work-related stuff lol. So we called it and I quit the game.
Then I was like 'well, I could idle and level my mag up for the last little bit, that doesn't require any focus.' So I tried to log in again, went fine, picked my character, picked Block 1 and then it immediately gave me the No100 connection error.
Hm, okay... try block 2. It didnt boot me once I reached the lobby, tried to create a room and got the error again.
Third time's a charm? Go to Block 3, created a room, its loading... and then the camera is facing the city skyline above Pioneer and its giving me the No100 error again.
The weirdest part is all 3 blocks are very consistent and wind up with their own unique results like this every time.
Tried a different character, same problem.
Tried making a new character, results on each block are slightly different (I can progress a bit further in each) but error still occurs.
Started game without launcher. Used update button on launcher. Used patch download in main menu. Uninstalled and reinstalled. Nope.
Uninstalled the game, went into the registry, and deleted anything related to 'ultima' or 'psobb' that I could find. Reinstalled game. Nope.
Nothing changed in the 10 minutes between exiting the game after my session with my nephew and me starting up the game again to idly feed my mag. This was yesterday and I'm back in the office with the same issue, so I really doubt whatever is affecting the game is at least not my internet connection here - we went close to 3 hours without any hiccups, going in and out of rooms to start new government quests together. I saw this topic and how it was fixed without knowing really how and it seemed to be a registry issue. I'm not sure if I can run a registry cleanup of any kind on this computer but I can manually go through it.
Can't run the app as administrator so I cant give you a crash dump. Just wondering if you might have figured out the root cause of this one since this topic was created. If I can't fix it its no big deal.