When developing modular applications in Adobe Flex, its critical to ensure that all resources are available for the module and the application that loads it.
You will most likely not get any errormessage indicating the problem, the module will just never complete its creation flow and leave your application hanging somewhere in mid-air between the initialized and the creationComplete event.
The error handling in the ModuleManager and the ModuleLoader are to be honest, not particularly well written at this point (as of Flex 3 Beta 3, Milestone 4) and I expect that the entire mx.modules package is scheduled for an overhaul during the current and last development iteration prior to the emergence of the release candidates (if any) and the first release.
Anyways, back to the issue about missing resources causing the Module creation flow to halt… even the emittance of a style sheet reference used by the module will cause the creation to halt and fail in Flash’s silent, but deadly manner (I never liked that paradigm and I am sad to find it all over the place, even here in one of the mission-critical parts of the framework).
I would very much prefer not to have to modify the source code for frameworks and/or 3rd-party products used by production systems, but if the mx.Modules don’t receive a lot of “love” from the Flex team prior to release, I will have to in order to get the required stability and robustness.
I would like to mention at this point however, that we have decided to use Flex 3 for production level systems at a very early point, and in general this has been a hugely positive experience (please read previous posts about our Beta experiences) and I have not regretted this decision at any point.
Here you can read more about how to create modular applications with Adobe Flex if you have any interest in this…