Selection activated by characteristics of the header material

What causes this issue?

You have activated selection by characteristics of the header material.

System Response

After exiting the current screen by choosing 'Execute', you can further
restrict your selection using characteristic values of the header
material.

How to fix this error?

Complete your entries on this screen and exit by choosing 'Execute'. If
you do not want to select by characteristic values, choose
'Characteristic selection' again to deactivate selection by
characteristics.

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.