Does "reservecache" take away memory for the database?
Not in a way that would cause this problem. The size limit here is on the
remembered running order area in the scratch partition, which isn't affected by reservecache.
The problem is that this remembered running order takes space for every reference to every song, not just every song. So if you play your whole player, and you've got five references to every song (perhaps in auto-soup-generated playlists), you'll hit the limit before a person with only three references per song does. That might be the difference between one person's 6000 and another's 7600.
You guys who are having the problem, have you got lots of references to each song? Say, one in an Artists playlist, one in Artist/Album, one in Genre, and so on?
Peter