OpenSAML user discussion

I think that is indeed the problem.
I have used Weblogic (10.x) servers with opensaml and xmlsecurity without 
running into your problem.
by default, Weblogic has a version of opensaml on its server's classpath (one 
of the many weblogic modules jars).
I also have xmlsecurity on the server's classpath. 
I guess that is why I don't have the same problem.

I guess you should try to put xmlsecurity on your server's classpath.
If not possible,
maybe you can try adding all jars to WEB-INF/lib and set the 
prefer-web-inf-classes option in the weblogic.xml deployment descriptor.
or if you are using an ear to deploy, better is to use the more fine-grained 
prefer-application-packages in weblogic-application.xml

Hope that helps,

Frederik