You need to install JRE 1.3.0_02, 1.3.1_10 and 1.4.2_04.  Using Web Start 1.4.2_04, we cannot get any property files to load if JRE 1.3.0_02 is used.  We specify <j2se version="1.3*"/> because our application contains many sub-applications which were built with components that are not 1.4 compatible yet.  If you go into Web Start preferences and uncheck 1.3.0_02, it works fine.  Unfortunately, 1.3.0_02 is what we used to install if a user did not have a 1.3 JRE (it was an applet using the Java Plug-in) and that version still works with the Java Plug-in.  I have gone through the forums and tried every known way to load properties and it just doesn't work with Web Start 1.4.2_04 if 1.3.0_02 is picked as the JRE.  This is going to require manual intervention of >10,000 users to work.

As a side note, if 1.3.1_10 happens to show up in the Preferences before 1.3.0_02, it picks that version up and works fine.