I continue, with no luck, to seek a solution.
When I try to BROWSE in MC17 to Restore my library, I am able to navigate to the indicated folder (C:\Documents and Settings\John\My Documents\J River\Media Center 17). Problem is, that folder contains only a couple of partial libraries created since I registered MC17. It does NOT contain the complete libraries created by MC15 -- including the one I would like to restore/install/import into MC17.
I am NOT ABLE to BROWSE to MC15 from the MC17 window because the indicated folder (C:\Documents and Settings\John\Application Data\J River\Media Center 15) DOES NOT EXIST as I attempt to browse. That is the "address" of the library folders for MC15, according to my Windows search engine, but there is NO "Application Data" folder inside the "John" folder, inside "Documents and Settings".
I tried everything I can think of, including attempting to copy-and-paste the library address from MC15 into MC17, but that does not work, either.
Surely, there must be a provision to transfer a library from an older version of Media Center into a newer version.