Function is only possible for active users using user management

What causes this issue?

Changes to active BCS users are only possible in user administration.
This ensures consistency between the SAP user and BCS user as both users
can only be changes together.

System Response

How to fix this error?

To change the active BCS user, use the functions in the user
administration. If you use "central user administration", then you must
make the changes on the central instance.

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.