SAP Message 5A028 - Relationship structure & & & not allowed

Diagnosis
This error occurs when the relationship you are trying to create issomehow in conflict with, or contradicts, another relationship thatalready exists.
For example, this message would appear if you try to create arelationship between two organizational units, and one of the unitsalready has this relationship with another organizational unit, locatedon a different level of the structure. This message also appears if youtry to relate an object to itself.

System Response
The system will not allow you to create the relationship.

Procedure
Make sure you have selected the correct objects for the relationship.

662889EBP 3.5+: Purchaser responsibility for themselves