Trading partner is reset in general ledger view

What causes this issue?

You are executing a cross-company code posting between more than two
involved company codes.
In the entry view, the logic for determining the trading partner is
dependent on the first company code, that is, the leading company code,
whereas in the general ledger view, determination of the trading partner
for the company code clearing items is coupled with determination of the
partner entities of document splitting. The heuristic for determining
the partner assignments in company code clearing items is explained in
SAP Note 973342.
You are using a document type to which a business transaction variant is
assigned that is not intended for projection of account assignments to a
company code with a leading item category, but rather assigns the
company code clearing item on the basis of the respective partial
document.

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?

If possible, execute cross-company code transactions using such a
business transaction variant only between two company codes.
Alternatively, specify the partner assignments manually in the entry
view.
Another alternative is to enter, as the first document item, the line
item of the company code to which the following company codes are to
clear. This also ensures that the sorting and trading partner
determination described in SAP Note 973342 are used in the entry view.

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.