Well, obviously LyX sees the package. You're saying that in Tools > Preferences > Look and Feel > Display, the drop-down list next to "Instant Preview" is grayed out? Or is the "Off" option alive but "On" and "No math" grayed out?
In your local LyX settings directory (Help > About LyX > User directory points to it if you don't know where it is), there's a text file named "preferences". In the "MISC" section, try inserting the line \preview on (when LyX is not running), then start LyX and see if (a) preview happens by any chance to work and (b) whether the list in the preferences section has somehow magically activated itself. /Paul
