Jazz and Big Band KP2 edition does not require Garritan Studio. Studio was an application designed to interface between notation programs and the KP1 version of GPO and JABB. With the multiport instrument hosting available in KP2, it became not so necessary. KP2 updates JABB with numerous bugfixes and performance enhancements.
The error message you're receiving is because the Studio application is looking for an older filetype that designated JABB version 1.
Your JABB runs fine in Kontakt Player 2 right? So no worries