Unique reconciliation key for &1 &2 cannot be determined

What causes this issue?

No unique reconciliation key can be determined for
the run with run date &V1& and run identification &V2&.

System Response

It is not possible to save the data.

How to fix this error?

You have to do more than just change the
run identification at the sixth position.
Example:
You have executed a dunning proposal run with the run ID "MAHNL1" and
want to name a second dunning proposal run on the same day "MAHNL2".
The system rejects this run ID.
Change at least one of the first <ZH>five</> characters of the run ID,
for example, "MAHN21".

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.