I do not have an answer, but I have a 2002 RX 300 and have experienced the same issue. Shortly before the problem happened, the nav system was acting funny (telling me I was on a street across town) - then it went blank - now it says either Disc Error or Program Disc Installed. A helpful service assistant at Lexus of Greenwich told me that mine was the second 2002 RX 300 she saw this week with the exact same problem and told me it would be close to $1,100 to fix. I am wondering if these cars have a self destruct mech. in them so service depts can get some more $$$...
Mike, August 2008