Hi
I had that happen on my E32 740i a number of times after the car had done 75-80k miles. Initially the dealer advised that an electrical spike had caused it and if I parked, left the car for 45-60 and came back to it, the system would reset. This certainly appeared to be the case, it was also slightly improved by checking and changing the gearbox oil (sealed for life at the factory!). Eventually at 130k miles the gearbox gave up the ghost and I had it rebuilt.
I had also had this message come up on E38 B12 5.7 and that lead to the car being off the road for 7 weeks while BMW GB sourced a new ECU from Alpina. I'd only had the car 4 weeks and I have to say GB were B useless. In the end I rang the Alpina factory, spoke to somebody in their parts dept, in English, and got a straight answer in 5 mins. He knew the car, the part, when it was ordered and when it would reach Bracknell (GB Parts). After that episode, I met Kris at Goodwood and any future questions I had, I phoned him direct.
Hope this helps and the best of luck.
Joni P