OK, I again ran into this problem. From my point of view it’s a bug in Studio. When you edit a UI screen in Studio, Studio instead of overwriting the original UI screen sometimes tries to create a new UI screen with the same ID (screen name) and the same agent. And Studio complains about that. The workaround is pretty simple: Select any agent (there are four: empty, PHONE, DESKTOP, TABLET) that you do not use at that moment, then Studio creates a new UI screen with the same ID (screen name) but with a different agent. Afterwards you can delete the old screen and set correct agent or delete the the agent setting.