Business partner &1 is already assigned in role &2

What causes this issue?

Section/sequence number of entry: &V3&
Partner &V1& is already assigned in the role &V2& (&V4&).

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?

Correct the validity of the partner assignment.

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.