355F1 flashing 6th gear indicator

a new problem has raised it's ugly head on my 99' 355F1 spider it seems like 7/10 of the time I engage 6th gear to cruise on the highway after between 20-60 seconds the gear indicator LED starts to flash the nubmer 6 at me. If I downshift to 5th or any other gear everything works and runs perfectly. Also I have tried selecting neutral and then reselecting 6th like the owners manual states but it usually just starts flashing again after the 20-60 second time interval. I have also noticed that if it does not flash after 60 seconds then it does not flash for as long as the gear is selected as I have been able to cruise about 20 minutes with no flashing in that same gear before I had to downshift to come to a stop. Has anybody else had this problem in the past? What are some of the things I should be checking for? Thanks in advance