So as I've alluded to before, the plug-in does not handle MU installations properly. Rather than instruct the user that it's not supported (in non-pro versions), it does not show up at all and a call directly to the configuration page throws an error. Thus if my settings are lost, I must manually add the code to disable the MU check so I can get in to enter in my registration code.
On top of that, even after getting the above sorted out, if I attempt to use the plug-in on a new site created in the same network, I have the problem all over again, so I must disable the MU check permanently. Fortunately this doesn't seem to have any complications.