2002 S8 Gearbox in 'Limp Home' mode
I have developed the same problem, but it is intermittent.
Audi main dealer took £500 off me for saying that the cover box was cracked and was allowing in moisture - they replaced the box and since thin I get the Safe Mode everytime the car is started, After running it for a few minutes and trying several more times it usually comes right and is perfectly drivable, until the next time it has stood for a while - then, same routine all over again.
Having looked under the bonnet I do see that there is always a lot of condensation on the lower surface of the bonnet...
Have drained the wheel arch tubes and made sure that the main drains under the aircon intake box are clear - they are.
Audi now want £1,100 for a new ECU for the Gearbox, but cannot promise that this will fix the problem.
Otherwise, the car at 55K miles is perfect, but I am forming an opinion that I should dump it and get something else, as the forums are full of electronic problem issues and people are saying that these are a one way street to losing money...
Any bright ideas out there for this 1st time user of this website community?