Same problem here on my IS 200 - half the time my Sat nav unit functions then the other half it stops reading the CD & has one of a few error messages 'CD unreadable', 'insert disc, check door' etc.
I would be keen to hear how I get this fixed - Lexus quoted £2K plus to replace or £1k for an exchange unit (if available). I can get Sat Nav & GPS Gatso software for £200 !!!
GB