The relationship &1 is not internal or external

What causes this issue?

Although relationship &V1& is maintained in the table of possible
relationships (T778V), it is valid neither for an internal object type
(T777E) nor as an external relationship (T77EV).

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?

Delete the superfluous relationship &V1& from table T778V, or define
the object types for which the relationship is valid.

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.