I was configuring our new Cisco ASA 5510 firewall today, as part of a major infrastructure upgrade. I'm pretty comfortable with the Cisco IOS, but I still prefer the GUI for the basic set up, using command line to tweak the finer or more complex configurations. However, straight out of the box, I had a very hard time getting the ASDM to load. Being familiar with the PDM from the PIX range of firewalls, I should have guessed the problem straight away. Essentially, whatever problem you're having with the ASDM, whether it's not loading, not reading the configuration or whatever, the answer is likely to be "uninstall your current version of Java, google java 1.4.2, install it, try again". It was the same with the PDM, and guess what? It's the same with the ASDM.