CDI or Contexts and Dependency Injection at a surface level, is the ability to use annotations like @Inject, @autowired and so on. If you're not familiar with it, checkout this Wiki page - anyway, what I was trying to verify is that you weren't running activiti-cdi, cdi, and spring's version of cdi. That would cause collisions and most likely lead to the error you're seeing. Your swapping of the XML configuration wouldn't fix this if your application is missing dependencies required to use the beans, or if there are collisions between multiple dependencies.
So you're correct that using Spring is not required; however, spring-beans is a compile dependency of Activiti, and thus spring-core package is as well. Which, could potentially be the problem, because I don't see those in your list of jars and they're used for dependency injection - but I'm not sure missing those dependencies would cause this particular error. However, you should include those, to confirm that theory.
Has your Activiti installation ever worked, or is this a blocking error that hasn't allowed the server to fully boot?
Potentially helpful:
Someone on another blog post had a very similar issue; there solution might help. There are a few other posts about the same exception, but they're less robust and boil down to collisions of dependency injection frameworks.
-JEarles
