Ok, I no longer have the problem. The bad part though is that I don't know what fixed it. I've spent the last two days trying out about half a dozen different Glassfish versions. In the end I just uninstalled all JDKs and Glassfish I had installed, reinstalled JSAS 9.0_01 from the Sun website, and basically redid everything from scratch. Web service invocations are working fine now.
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