Some time ago I posted about or 99 Passat 1.8 with the triptronic that worked just fin in automatic, but would not switch to manual.
Well, it turns out that the problem was the black plastic "bezel" that surrounds the gear shift shaft. There is a little magnet on it that lets the car know where it is. Ours had gotten bent, so the magnet wasn't aligned with the sensor.
We had the bezel replaced and now the car shifts fine.
Bob