Had the same error on WinXP.
Don't know if this is significant or not, but here's the goods on system info:
Now, here's the info I haven't seen before, may or may not be relevant.
I'm using eclipse 3 (Milestone 6). Anyone else having this problem using an IDE?
Also, I had J2EE 1.4 installed, but uninstalled it to put 1.3.1 on. Again, didn't see that anyone had "downgraded" their level of J2EE