Why is this question here? That is not a jboss component.
This error occurred while using the jboss-4.0.3sp1-installer.jnlp Java Web Start installer.
This problem can be side stepped by downloading JDK1.5.0_02 seperately (instead of having the installer try to do it from JDK 4) and then downloading the .jnlp file seperately and running "javaws jboss-...jnlp".
But for the fact Sun's site gives an error when you try to download JDK1.5.0_2:
Due to exceptionally high demand for our most recent product offerings, our site is extremely busy right now. In order to provide you the best possible service, we ask that you please try again later.
Be assured that we continue enhancing our systems to serve you better.
We appreciate your patronage and patience. "
That's the power of Sun's enterprise systems!