Object validity: &1-&2, partner only assigned in period &3-&4

What causes this issue?

The business partner is only assigned to the object/contract in the
period &V3&-&V4&. However, the object (or contract) has a validity
period from &V1&-&V2&. The business partner is therefore not assigned to
the object or contract at any time when it is actually valid.

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?

This is a warning message.
If you have intentionally assigned the partner
in the defined period (for example because the contract will probably be
extended) you do not need to do anything.
However, if the assignment period is unintentionally outside the
validity period, correct your entries.

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.