I would try uninstalling again, then manually deleting the J River folder and fire up regedit (or a
good regcleaner) to clean the registry of any MC entries. I managed to come up with the following list of keys/subkeys, not sure if it's 100% but should sufficiently remove the core entries.
HKEY_LOCAL_MACHINE\Software\JRiver\BuyButton\2.0
HKEY_LOCAL_MACHINE\Software\JRiver\BuyButton
HKEY_CURRENT_USER\Software\JRiver\CDLabeler\FrameSettings
HKEY_CURRENT_USER\Software\JRiver\CDLabeler\Settings
HKEY_CURRENT_USER\Software\JRiver\CDLabeler
HKEY_CLASSES_ROOT\.MJL
HKEY_CLASSES_ROOT\CDLabeler.Document
HKEY_CURRENT_USER\Software\JRiver\Media Jukebox\MCBars
HKEY_CURRENT_USER\Software\JRiver\Media Jukebox\PlaybackEngine
HKEY_CURRENT_USER\Software\JRiver\Media Jukebox\Plugins
HKEY_CURRENT_USER\Software\JRiver\Media Jukebox\Properties
HKEY_CURRENT_USER\Software\JRiver\Media Jukebox\TV Settings
HKEY_CURRENT_USER\Software\JRiver\Media Jukebox\View Info
HKEY_CURRENT_USER\Software\JRiver\Media Jukebox
HKEY_LOCAL_MACHINE\Software\JRiver\Media Jukebox\CD Reader
HKEY_LOCAL_MACHINE\Software\JRiver\Media Jukebox\CD Writer
HKEY_LOCAL_MACHINE\Software\JRiver\Media Jukebox\Plugins
HKEY_LOCAL_MACHINE\Software\JRiver\Media Jukebox\Properties
HKEY_LOCAL_MACHINE\Software\JRiver\Media Jukebox
After that, reboot, reinstall and reimport your library.
If that won't fix it, then you have a rogue file somewhere and someone with more in-depth knowledge of MC will need to advise from there
Hope it helps.
Rob