SAP Message 6G120 - Define only one development system for the structure

Diagnosis
You have entered more than one system as the development system for thestructure of the System Administration Assistant.

System Response
The development system must be unique.

Procedure
Correct your entry, and choose one system as the development system forthe structure.
Generally, this is the current system or the system in which youconfigure which systems you want to administrate using the SystemAdministration Assistant.