When I purchased the program, it allowed me to open/download a registration key. The registration key file shows up as media jukebox (5-digit number) when I download it to my desktop. Alternatively, I get to this file through an email link sent by Media Jukebox that is a 25 digit number (AMBZ9-......). I open the file and it says "license ... successfully installed" but then a second window opens saying "A license for your JRiver software has been automatically installed. You will find your Install Key in a separate browser window (probably behind this one). To save it, right click on the link and use the "Save As" option." No second window opens. If I run media jukebox at this point, it is still the trial version, indicating to me that, although the registration/license file has worked, a second installation key file is still needed that I do not receive.
I have tried work-around like you suggested, retore license, and all of the other suggestions, but the furthest I can successfully get is to the point where I download a registration key. Still the conversion to the PLUS version does not happen.