Use a multimeter instead of a voltage detector. Those things are ok for a quick check but can be very unreliable.
Is it possbile that the light is on a three way switch and the other switch is off someplace else? Also, are you sure the light is on the same circuit as the outlets? Do you know where the light switch feed comes from?
I hate that. Some genius was either too cheap or too lazy to wire it correctly and just tied it into an unrelated circuit.