As I hinted at yesterday Genius playlists are a new "species" of playlist. Several scripts are affected by their inability to correctly distinguish Genius playlists from other playlist types. I will be working on fixes for them in the coming days. I think, in fact, that you can pretty much attribute any failings of AppleScripts that did work before iTunes 8 to the appearance of one or more Genius playlists. You may want to verify this by shutting Genius off and trying the errant script again. While some AppleScript behaviors have been updated/fixed in iTunes 8, I have not (yet) noticed any new AppleScript features that would otherwise cause scripts to error.