Hello, so you were able to get the device to come to ready when you would powercycle and unplug from the network correct? If that is the case something is hitting the machine from the network. I believe you stated that you cleared the print ques, did you clear the que from the server? Or on the users workstation? If from the server, I would try to pin point which users print to it and check their ques on their workstations. Actually came across this recently were we checked que on server and their were no jobs, we even stopped the spooler, and restarted, with no help, but I was able to trick the machine to print a document before the error came back, then I was able pin pointe the user and found jobs in their que. The conclusion I came to was that whoever installed their printer did it locally, and did not pull from the server, hence why the que on the server was empty.
Hope this helps.....