Error code 278 means Roblox disconnected you because the game was idle for 20 minutes. Roblox ends inactive sessions automatically to free server slots for other players, and the 20-minute limit applies across all experiences.
If 278 appears while you were actively playing, check that your inputs are reaching the game, since a frozen client or a lost connection can look like idleness to the server. Restart the client and check your connection if active play keeps ending in a 278.
Can I turn off the idle kick? No. The 20-minute idle limit is set by Roblox and cannot be disabled in settings or by the game's developer.
Is error 278 a ban? No. It is an automatic disconnect for inactivity, and it carries no penalty. You can rejoin immediately.
Does moving the mouse count as activity? Any real input to the game counts, including moving, chatting, or clicking in the game window. Simply having the window open does not.