A build check error in the area "Other problems". An error: the game cannot be published until it is fixed.
The build check runs on every game LobbyLab builds, and each problem it finds has a stable code, the exact message, the file and line when it names one, and a link to this page.
What the check looks at
A problem the check reported without a more specific code.
How to fix it
Read the message: it says what failed. Fix that and run the check again.
See also: every error code, the API reference and the docs.