this is a very common problem on IS's.
Hate to tell you to go search on the UK forums - so I have done it for you!
all the topics on UK Lexus Owners Club regarding IS CD ERR3 problem ;)
basically, what you will find is that it is a common problem, which is covered by the warranty.
In the UK, the warranty has been extended to 4 years for the stereo - because of this exact problem.
How old is your car?