I have a wireless networked HP printer and was getting this error: Unable to communicate with device (code=12). I ran hp-check, hp-setup, hp-plugin, etc. After a few days' worth of frustration, I've figured it out.
The key was this: http://hplipopensource.com/node/216
So after running
snmpwalk -Os -c public -v 1 ip.address.of.printer 184.108.40.206.220.127.116.11.18.104.22.168.7.0
I got this message: Timeout: No Response from ip.address.of.printer
Then I remembered...