It is probably a problem with your Java Web start Cache, where your downloaded repository jar files are stored. Clear the folder once, You can do so by opening Java Web start go to File --> Preferences -->Advanced. and download repository jars once again by clicking on your Integration repository link.
Also make sure you are using a recommended JDK version i.e. 1.4.2_07~1.4.2_09 for doing all this to avoid all known problems with the JRE versions.