I have a couple of Pix 515 and a couple of Pix 506. I have a user defined on these firewalls with the "Username" command. Before changing the password I had no problem accessing the firewalls with the GUI PDM. Since changing however, I pass the authentication box fine, I get the Loading Pix Device Manager screen (which always comes up), but then it just hangs on that screen. It never brings up the Firewall GUI.
I have tried this on both the 515 and the 506 with the same results.