Invalid assignment

What causes this issue?

You assigned an object as a superordinate object, but according to
Customizing settings, this object is not allowed to be superior to the
current object.

System Response

The assignment cannot be saved in this form.
Possible reasons for this include:
The object you want as a superordingate object is not at a higher
position in the hierarchy then the current object.
The object you want as a superordingate object is in a completely
different hierarchy.
You skipped over one or more hierarchy levels.

How to fix this error?

Assign a valid superordinate object to the current object.

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.