[Patrickwhite]

Are you getting any response when you deploy? If the robot does nothing, the robot is probably quitting unexpectedly, which you would receive. As for working with two photosensors, if you are dead set on using them (instead of other sensors or dead reckoning as has been suggested) I would place them directly adjacent to each other, so they can both be tripped by the tape at the same time and working with that. There may be some interference however (one receiving the reflected light from the other and returning a false positive) and it obviously won't be ideal.