Conversion of business partner GUID &1 into BP number failed

What causes this issue?

The business partners belonging to a contract are stored in an internal
format on the database and not in the outwardly visible business partner
number. Depending on whether you are reading from or writing to the
database, the business partner is automatically converted.
The system tried - unsuccessfully - to find the corresponding key. This
can indicate an inconsistency in business partner management.
In the short error message, the system also outputs the business partner
GUID. However, if this GUID is missing (you will note a larger space
between the words 'business partner GUID' and 'in'), the termination
resulted because the transfer field (in this case the BP GUID) is blank.
This should not be possible at this time because you are reading from
the database (this could mean a possible data inconsistency).

System Response

The system cannot verify the business partner for the contract and so
terminates processing.

How to fix this error?

Repeat the operation. If the problem occurs again, contact your system
administrator.

Procedure for System Administrators

Check if the business partner still exists. If the field (BP GUID) is
blank, check whether the entries for the contract on the database are
complete.

Error message extract from SAP system. Copyright SAP SE.