hplip is a problem. It's still a problem with rc2. HPLIP uses libusb to communicate with devices, CUPS uses usblp. While cups should be able to use libusb as well it is not, and the two devices do not communicate, for printing.
We have left HPLIP in because it does work for scanning and checking inklevels, but for now you will have to print through cups directly, using a printer that was set-up by cups.
Go to System>>Printing>>+ADD and use that printer set-up for your printing.