Was the 192.168.2.11 already configured ? If so, does the ACS have multiple interfaces ? Does any aaa from the concentrator ? If so, then you just might have to change the authentication server ip to 192.168.5.50, but be careful if its an operational concentrator. Changing the aaa-server might give problems. Anyway I'd sort out what for device 192.168.2.11 is.

If I understand your problem correctly, you have added the concentrator in the ACS and don't understand why the 192.168.2.11 is in the Concentrator config ? Please clarify your problem a bit.