As brought up in the forum at http://forum.springframework.org/showthread.php?t=49583, it looks like as of Castor 1.2, castor has changed the way their XMLClassDescriptorResolver behaves that is incompatible with the way CastorMarshaller.java is using it.
While loading the spring config you'll get the following exception:
Caused by: java.lang.NullPointerException
I think spring-ws's CastorMarshaller may need to change to use Castor's XMLContext instead of the resolver directly and when creating castor's Marshaller/Unmarshaller. I was able to do this with local changes and it works fine, but that would probably break pre-1.2 Castor so the real framework change would likely involve a bit more.