I had this problem happen the other day and it happened again today so i thought i'd see if anyone else has had the same problem or not. This has only happened twice ever, both within 4 days of eacher and under similar conditions. Whats been happening is when I've taken off from stationary in economy mode (not sure if thats just a coincidence or not) I'll be in first gear, and at the same rpm that it would usually change to second at it suddenly drops into neutral, I tried moving the shifter back to first aswell as moving it to neutral and then back into gear with no luck, after ~10 seconds it picks the gear back up and functions normally again. Anyone else had this happen? Or have an idea what would be causing this? Is this a sign of my auto box on its way out or a computer issue?\
Oh also, it's a 2001 series II sedan with 140,000 on the clock

Take the Neutral start Switch off the l/h side of the auto, clean it off and put a little wd40 in the hole where the shaft goes through, hook it back up and go for a ride.

Great thanks mate, I'll give it a shot and see how it goes

Unlikely to be the switch, Look at getting fluid levels checked and topped up. Could need ajustment. Try it in normal mode. Econ mode changes shift points early.