So I am still not clear for what the *.mjr file is good. It does not work on Windows nor on Mac.
The MJR files are the mechanism used to apply the license,
even when you do it from within the application by entering your license key. So, if you got it to work that way, it actually
did use an MJR file "behind the scenes".
Using an Install Key file like MC does may not be something you're used to, but it is actually a fairly common licensing method (particularly among "enterprise" applications). In the case of Media Center, the MJR file has to be opened by the Package Installer appropriate for your version of MC. This
usually happens automatically, but sometimes the OS doesn't associate the MJR file extension with the right version of Package Installer. This is most often the case if security software on the computer interferes with MC's ability to set its own File Asssociations, or if you try to run the MJR file before you've ever launched and used a particular version of MC (it always associates the MJR files with the last major version of MC to be running).
If this happens, you need to tell the OS to open it with the correct version.
You can fix this on Windows by following the instructions here (down near the bottom) for
How To Open A File In An Unassociated Program With Or Without Changing The File Association:
http://www.7tutorials.com/how-associate-file-type-or-protocol-programWhen you get down to the part where you click
Browse, then find and choose this application:
C:\Program Files (x86)\J River\Media Center 21\PackageInstaller.exeBe sure to choose the one for MC21, and not previous versions, or it won't work (this is almost certainly what was happening to you before - the License
was being installed, but by MC20, not MC21).
On Mac, the process is similar:
http://osxdaily.com/2013/08/08/change-default-application-open-files-mac-os-x/The Package Installer application on Mac OSX is located "inside" the Media Center 21.app package (apps on OSX are really just folders, you can show what is inside them by right clicking and choosing
Show Package Contents). The Package Installer is here for MC21 on OSX:
/Applications/Media Center 21.app/Contents/MacOS/PackageInstaller.appAgain, be careful that you aren't opening it with an older version's Package Installer.
For me, it worked completely correctly on every machine I tested with (Mac and Windows). I'm not sure why it doesn't associate sometimes like it should, but both Windows and Mac OSX "protect" against applications taking over file associations now, because fighting over stealing associations like PDF and whatnot is an annoying behavior of malware applications. So, in certain cases, it seems to not work correctly.
If you got it working by typing your registration code into MC directly, then don't worry about it. This does generate a new MJR file, and uses up one of your restores. But, as JohnT showed above in this thread, those can be reset by JRiver staff. That limit isn't there to stop you from using your license, it is to keep honest people honest (and prevent sharing licenses among many different people).