Live updating itunes
So, unless there's a better way, it looks like you've led me to the solution. Credit here goes to the answer above, by fartheraway.
I don't think I'd even need to turn live updating on and the off again.If then (after "fixing" one playlist) I go to a different 'live updating' playlist, I just disable, then enable the 'live updating', and the playlist seems to work again.This is very tedious, but better than recreating the playlist from scratch every time.One of the many great features of i Tunes is Smart Playlists.Smart Playlists let you automatically create playlists of songs that fit criteria that you define.
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I'm using i Tunes 11.0.1 on 64-bit Windows 7, and occasionally my smart playlists (with live updating set to on) stop updating.