“Some of the software for the printer is missing.”

There’s actually a discussion on Apple’s forum without an answer. The answer is beware of HP Printer downloads. Not all are compatible with the current Leopard (10.5.x). A number are only current for Tiger (10.4.x). If you download them and install them, you should consider using a time machine recovery of the Operating System. At least, I found that deleting them and recreating them didn’t always fix the problem by itself.

If you haven’t installed them, don’t do it until you back up the /Library/printers/hp directory (typically about ~650 MB). It will enable you to recover without a full backup of the operating system. Open a terminal and run the following command:

# mv hp hpbackup

If the HP drivers apply and things don’t work you can recover. You can simply do the following two command from a terminal session:

# rm -r hp
# mv hpbackup hp

If the HP drivers apply and things work you’re fine. You can delete the backup directory and its contents by using the following command in a terminal session:

# rm -r hpbackup