Are you getting a stack trace, or just a one-line error message? If it's a stack trace, you might show it to us -- perhaps it will give us some clues.
It's possible you've got a corrupted Java install; in particular, you may have a JVM from one JDK version trying to use the class library from another Java version. Copying files around from place to place, hacking registry keys by hand, etc. may lead to a situation like this. This is one of those times when uninstalling the Java software, then re-installing it, may help.