Business partner &1 is centrally locked

What causes this issue?

The "Central Lock" is set for business partner &V1&.

System Response

The business partner is locked for certain activities. Therefore it
cannot be assigned.

How to fix this error?

Select another business partner or remove the lock for the business
partner selected.

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.