355 gearbox warning light

Help! My 355 f1 has the red gearbox warning light on solid. Everything seems to work fine, except the rpm rises during shifts, in other words, no injector cutout. would probably over-rev if you were accelerating hard. Luckily I was driving easy when it first happened. The car is drive-able if I'm careful to back off the throttle before each shift. My normal Ferrari guy doesn't have access to an SD1 any longer. Wondering if anyone else has had this problem. I have been told it may need a control unit, but sometimes it is the engine ECU and sometimes it's the transmission one. Anyone had problems with this before? This happened once this winter when it was very cold, and went away for 4 months, but now it's solid.