If you get a "The specified module could not be found" when you try to load mtoa.mll, it is most likely a problem with your Maya environment settings.
First, check your script history. That will show you what version of mtoa Maya is trying to load. If you don't see the expected version, then I would check your MAYA_MODULE_PATH and the modules\mtoa.mod file in your Maya user folder.
Usually, Maya is trying to load the right mtoa.dll, but the environment variables are pointing to the wrong place. Check your Maya.env file.
I often see something like this:
Notice how there are two sets of settings. Maya reads the first ones only, which are for the wrong version of mtoa, and then mtoa fails to load with a "The specified module could not be found" error. Just delete the first two lines and everything should be ok.