Could not create default assessment

What causes this issue?

When you create a value assignment, the system automatically attempts
to create a default assessment.
The system was unable to create this default assessment as no unique
default assessment has been defined in Customizing.

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?

Check your Customizing settings (table TCG71) or notify your system
administrator.

Error message extract from SAP system. Copyright SAP SE.