Interesting. Hmm...
Make sure to do a class scan in Poseidon so that all the drivers are in fact loaded. Then make sure to Save your configuration and re-upload it to the Deneb's FlashROM. There's a Quick Setup menu option in Luciferin that automatically adds all Poseidon-related files to the upload queue.
Other things to note: Make sure fat95, NTFileSystem, and AmiCDFS are all in L: - these are the default handlers set in Trident to mount drives.
I also had to add a 1-second startup-delay on my global massstorage.class preferences to be able to boot with a Flash drive inserted.
One last possibility - not enough power. Can you add a self-powered hub?
