Well, that's simply confirms what we always said (when people reports that problem in our modules) that message can happen with any developer's modules too.
That error doesn't mean that module has a problem, it means that FSX, for some reason, cannot load it, and it's usually because of missing/corrupted system libraries, or some kind of conflict with other addons.
The only thing sure, it's the conflict is NOT between the Addon Manager.
We had a discussion about modules conflicts here:
http://www.fsdreamteam.com/forum/index.php/topic,12418.msg94357.html#msg94357Usually this error is caused by different 3rd party modules that have been linked using different Simconnect version, loaded at the same time, but that message it's a result of some checks I made on several popular 3rd party modules and, PMDG are the ones that use the SAME Simconnect as we do (which is the latest one for FSX), so we can safely exclude the cause of the error is conflict between PMDG and our modules. Besides, I always keep them installed so, if there was any conflict, it wouldn't go unnoticed.
But, of course, your error might be caused by ANOTHER module using a different Simconnect version, and there are some I listed in that post you might have and might try to disable to see if they are in conflict with the PMDG modules.
Something you can try too, is to rearrange the order of sections in the DLL.XML, to change the loading order, which sometimes has an effect on potential conflicts.