Hi
Forget the dealers.
I too had a similar problem and went to dealers who said they could not work out what was wrong...changed disc etc but kept giving CD error. They said they need to take the unit out and send it to the manufacturers to fix. Cost would be in range of £1,000 to £1,500.
Today I went to PC world, bought a CD lens cleaner for £15 and slotted it in ...twice. Now my Sat Nav is working perfectly.
Exhaust all options before you donate your hard earned cash to Lexus!
Ani