Enter a valid mode for each activity

What causes this issue?

You want to adopt a new or changed mode combination. However, the
definition of this mode combination is incomplete, which means that
activities exist without an assigned mode.

System Response

The system is not able to adopt the mode combination.

How to fix this error?

Assign a valid mode to each activity and choose <LS>Adopt</> if you
want to adopt the mode combination.
Choose <LS>Cancel</> if you do not want to adopt the combination
changes.

Procedure for System Administrators

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

Error message extract from SAP system. Copyright SAP SE.