A packed project library essentially contains only compiled code so, like an executable, it has to be run with the same major version of the run-time engine that it was built in.
You might want to look at creating a LabVIEW DLL from your code, you should be able to call that in a newer version of LabVIEW providing you have the correct version of the runtime engine installed? (I've never tried it but that's my understanding anyway)
LabVIEW Champion, CLA, CLED, CTD
(blog)