gear box light on, engine stalls

Hi all,

i have a alfa 156 selespeed, it seems that when the engine heats up to over 90 then the gear box light comes on and the engine stalls and wont start until its cooled down, have checked all the usual things but found nothing obvious the car is booked in for diagnostics on monday but am a little worried they wont find anything, just wondering if anyone has experienced anything similiar with there alfa's and had it resolved.