Profitability segment with ledger group &2 not permitted for G/L item &1.

What causes this issue?

You set the ledger group &V2& in the general ledger item &V1& and at the
same time derived or entered a profitability segment.
You are not permitted to post with a profitability segment in a ledger
group that is not contained in the leading ledger. In the standard
system, Controlling only adopts postings that are posted in the leading
ledger. If the posting has not been transferred to Controlling, it is
not possible for postings to take place in the profitability analysis,
since reconciliation between the profitability analysis and Contract
Accounts Receivable and Payable using transaction FPG7 is otherwise not
possible.
Additionally, posting to a profitability segment with a ledger group
that does not contain a leading ledger could lead to double postings in
the profitability analysis if you make similar postings either with or
without a ledger group that contain the leading leader.

System Response

The posting cannot be executed.

How to fix this error?

Do not derive a profitability segment if you are posting with a ledger
group that does not contain the leading ledger. If required, adjust the
settings for the CO default account assignments.

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.