It's hard to tell what's wrong. With your description of the problem, it appears that when struts-config.xml is parsed when struts servlet is loaded, some resource cannot be found.
Since the class loading in V3 is very different from that in V2, I'm not surprised that what works in V2 is not working in V3.
To narrow the problem, I'd suggest that you start with a minimum struts-config.xml and see if you can get the same error by gradually adding more elements to it.
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