Control Framework: Fatal error - GUI cannot be reached

What causes this issue?

When the Control Framework is started, the system checks whether the
installed GUI supports frontend components such as controls. This check
failed; the causes may be as follows:
1.) The program is running in the background
2.) A transaction was called using CALL TRANSACTION ... STARTING IN
BACKGROUND TASK.

System Response

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

How to fix this error?

Programs that run in the background cannot address controls on the
frontend. In this case, the application must either include a fallback
that does not depend on the user interface, or the program or
transaction must terminate itself.

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.