Source system cannot be deleted in Content system

What causes this issue?

If a source system is deleted in the Content system, the shadow tables
for all source system-dependent objects for this source system release
are also deleted. You can configure a user as a non-Content user by
using a SET-GET parameter. You can then use this user to delete the
system, and then the above-named objects are not changed during
deletion.

System Response

The function is completed.

How to fix this error?

Logon as user ACTIVATE, and repeat your actions.

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.