Have you seen this one flash on the screen accompanied by the sound of a ding, "Cannot Read Data, Check Navigation Card"

So I hit the MAP button and it disappeared and never happened since. Any clues as to what's going on?

I was probably driving too fast that the hard drive read heads were not able to keep up with the car

 

I got the same message once years ago on early software. The system rebooted automatically. I was not going fast but in some tiny lanes. Never saw it again. I had one other early instance where all of my stored places were lost – much more annoying.

I gave up complaining to Lexus - too much effort for zero gain.

For example I complained about the time/date log on the NAV which is still an hour out half of the year because the system doesn't correct for daylight savings (or vice versa?) automatically and there is NO manual adjustment on the GS but there is on the LS! I guess they figured it was OK for GS drivers to be an hour out! Hardly important but I couldn't get anyone in Lexus to even understand that. At the same time Lexus also lied about having any problems (other than mine) with wheel vibration and hesitant acceleration on early GS 400's until I mentioned the terms of the lemon law. They were obviously too busy writing the secret TSBs - you had to know that they existed to get them performed.