Error code 600 in Roblox usually occurs when there's a connection issue preventing you from joining a game or experiencing a server problem. It can happen due to internet instability, outdated Roblox client, or server maintenance. To fix it, try restarting your router, updating Roblox to the latest version, clearing the cache, or checking Roblox's server status for any ongoing issues. If the problem persists, logging out and back into your Roblox account or reinstalling the app might help resolve the issue.