I'm in the process of upgrading to Flex 4, and I have a run-time exception when the application loads. The problem occurs when the SystemManager tries to initialize the mixins. In the SystemManager code, I see that it gets the list of mixins and then uses getDefinitionByName to get the class and call its init method. The problem is that one of the classes cannot be found, so the method returns null and the SystemManager fails when trying to use it (SystemManager, lines 2612-2622).
What I don't understand is why it can't find the class if just a few lines before it identified it as a mixin, which means it has access to it, and what can I do to fix the situation?