Bachus,
In YEM, did you checked the 'LSB' of your packs ? (in 'My Packs', select a pack, then click on the '>' button at the top, then 'Change Bank Select LSB')
In theory, each pack should automatically receive a different LSB, but if two packs have the same LSB symptoms like the one you described can happen ('empty registration', conflit between two packs, etc...)
The same thing can happens if you created your own registrations from packs, removed the pack, reinstalled it (YEM could have changed the LSB without noticing you…) , your existing registrations 'lost' their link with the voices…
To double-check, on the Genos there's an option that allow you to display the 'Voice Number' (LSB/MSB/Prog #) …
Benoit