Have you recently installed MusicMatch Jukebox?
If so, go to Start>Run and
key in:
msconfig
Click on OK or hit ENTER
Click on the Startup tab and click in the checkbox (to clear the
checkmark)
beside any and all entries relating to MusicMatch. Click on Apply then
OK.
When you next restart your computer, MusicMatch won't load and run in
the
background at startup (which is not necessary to have it do.......you
can
simply open the program manually when you want to use it), and that
should
solve the ShellIconHiddenWindow message at shutdown.
Seems like version 8 thru 10 of MusicMatch is pretty buggy.
Google; Musicmatch ShelliconHiddenWindow