No ideas? I think it might have something to do with the classloader settings (or lack thereof) for the jbpm service archive - if it was loading classes from a different class repository than the webapp that's signaling the process, and not loading first from the sar classpath I can theorize why that might cause this error. But I'm still trying to figure out what to do about it.
You say the problem only appears when you get a JAXR connection factory from within an action handler. Handlers are loaded with the process class loader, whose parent is the loader for the jBPM library (i.e. the service archive loader). The context class loader is skipped (the classes and libraries in your webapp are not searched).
In the end you don't specify where you actually place the libraries. That'd be useful. Right now I'd package them in the jBPM service archive (if you only use JAXR in jBPM processes) or put them in the lib/ subdirectory of the JBoss configuration you are using (if you use JAXR in other applications).
Thanks a lot, Alejandro. That explains and helps a lot - particularly your explanation of why the context class loader isn't being used. I've been up and down all the documentation of JBoss classloading that I could find and hadn't figured that out - I'm relatively new to JBoss.
I managed to get things working by putting my uddi and other ws calls in another service archive and calling them from jbpm through the exposed service interfaces.
Thanks for your help!