Just bought a used RX330 2004 a couple of weeks ago, read about the secret nav menu and just had to get in there, as many others on this forum, unfortunately i changed the "Loading" program from AUS TAB or something (I live in Australia and got the Australian maps etc) to US TAB and got hit by the fatal screen asking me to insert the correct disk.
Checked online, did everything everyone suggested, made a copy of the DVD, reinserted, turned off then on, disconnected battery overnight, disconnected ECU, called up Lexus, disconnected fuses overnight etc and nothing worked.

The solution: it's just as simple as the message states, there is no secret "fix disk", and no your ECU is NOT fried and you don't need a brand new one for $5,000 as several Lexus dealers suggested, all what you need to do is find any version of the map you selected, burn that onto a DVD and insert it, then using the secret menu (for the last time for sure!) switch back to your country's map, so in my case I downloaded the first US map i found, inserted the DVD, updated successfully, then from the secret menu switched back to the AUS TAB map.

Very interestingly is that the servicemen in Lexus that i've spoken with genuinely had no idea what I'm talking about when i ask about the secret menu, that's why the easiest fix to them was "we'll have to install a new ECU for you" not sure if this is the case in the US or not.

I just wanted to share this on this forum and give you guys some hope that there is a solution that costs nothing, all you have to do is remember which map you selected from the secret menu and find it on a torent site, I ran a search and found Russia, Eastern Europe, US and Australia, no luck with Japan but im sure it must be out there somewhere.

Hope this helps!