Controlling Area not available in list of NOT ASSIGN for Settlemnt No.Range

Hi Gurus,

I am not able to see the particular Controlling Area in the list of NOT ASSIGNED for "Number Range for Settlement documents CO objects" for object 'CO_ABRECHN' in SNUM T-Code. Other controlling area are available there.

What is missing in configuration?

Thanks in Advance.

Abhijit.