Lexis250

I've had my Lexus IS200 Sport for a while now and it has been beautiful and worked excellently except for last week when the Sat Nav started playing up. I have a DVD Sat Nav (2002 version) and the screen is showing the following message "UNABLE TO READ Data - Check if map DVD is correct" Has anybody experienced such problems before or got any solutions? Does anyone know where the DVD for the Sat Nav is located? Any solutions will be appreciated. Cheers.