Java Security

I'm trying to learn to use JAXB..

Well.. the XML schema binding and stuff seems to go well, but when i try to use the classes (only trying to instantiate the "main" object of my XML structure), i get the following exception :

java.lang.SecurityException: class "javax.xml.namespace.NamespaceContext"'s signer information does not match signer information of other classes in the same package

I read some posts on the forums and some people (with a 'signer-problem') said that there's probably two different versions of the class that's causing the exception on the classpath..

One NamespaceContext -class seems to be in the namespaces.jar that comes with the Java Web Services Development Pack, but where is the other ?

And even if i knew where both of them are (if that's even the problem), what could i do about it ? I probably can't change the system libraries ? :)

This has been driving me nuts all day long, but i'd like to get JAXB to work, so maybe you could help me out here?

Maybe i messed something up while clicking on "next" during the installation process ? :)

And no one else seemed to have had any trouble with the NamespaceContext class !