hi Tim,
With the release of the CityEngine 2011, Esri has created new License Server software (based on their existing FlexNet technology) for the CityEngine, but for floating licenses (concurrent use), the old License Server you have should work fine too.
Though, you will need to get a new floating license file from Esri which activates the new features.
By 'code', do you mean that you got Activation Codes ? Because Activation Codes create nodelocked licenses, thus are of no use for you.
Please let me know.