CUA definition is inconsistent; for repair, see long text

What causes this issue?

The CUA definition is inconsistent, because
the ALE model is inconsistent.
For the ALE model, Central User Administration requires a uniquely
defined central system (only a central system). All child systems must
also be included in a CUA only once (no duplicated systems).
Some child systems were deleted from the ALE model, while they are still
in the CUA model
The central system of the ALE model does not match the central system of
the CUA model
The CUA model exists, but the ALE model does not

System Response

How to fix this error?

To resolve the inconsistency of the ALE model, you can either change or
create the ALE model in transaction BD64 or save the CUA view in
transaction SCUA, so that the ALE model is regenerated in accordance
with it. If you perform the adjustment in transaction SCUA, you can
either save the CUA model immediately or first change and then save it.
If you want to remove some child systems from the CUA, you should first
remove these in the CUA model on the initial screen of the transaction
SCUA by choosing <ZK>Delete</>, both in the central and relevant child
systems.

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.