If the aeroplane is not moving THROUGH THE AIR it cannot fly. If it's on a conveyor belt, the belt doesn't care what speed the air is moving and the belt won't move the air to move (OK, it could be argued that the "boundry layer" of air to the belt has a velocity, but realistically it's enough to ignore in this case).
All the time the belt is moving "backwards" at the same speed the a/c wing is moving forwards, nothing will happpen.
Think of yourself running on a treadmill (unpleasent thought, I know...!)....when "running" at the same speed as the belt, you are stationary - your relative wind = 0, therefore no angle of attack, therefore no lift.
Good one though, has got me thinking about how to word an answer.
tKF