Have the same problem. Am using a 2010 MacBook Pro running Mac OS X Snow Leopard v10.6.8. Message started popping up the other day even if I did not install/uninstall printers recently (last one was about a year and a half ago). In fact, I did not change any setting or install anything new in the few days previous to that... except perhaps update my Adobe Flash Player (the usual update).
The thing is, I don't have the com.hp.printeragent.plist in my LaunchAgents folder tho I have an HP LaserJet P1505 and HP LaserJet P1102 installed What I do have in that LaunchAgents folder are a couple of *.adobe.*.plist files
Any other ideas? The only other fix is to disable the firewall as suggested at another thread but of course I'd rather not do that!
Thanks in advance!
P.S. I discovered that if I click on the Advance Settings of the Firewall and right click on printerAgent (of which there is more than one entry, one for each time I had to reply to that printerAgent message at boot up) to get "Show in Finder", this leads me to a printerAgent file in a folder in Library/Printers/hp/laserjet. Just thought I'd mention this in case it would be useful...