Expression Pedal Issues

I'm new to MainStage. When I create a patch by selecting software instrument, the classic roads comes up as default. The expression pedal will bring the volume up and down perfectly. When I add channels i.e. strings, the expression pedal dosent work on any of the other channels. I've gone into midi input and selected filter and unassigned, still nothing. The expression dial at the top of the channel shows the volume dial going from 0 to 127 but the volume is not changing. It only works on channel 1 with the classic rhoads. I tried switching channel 1 to a string patch, but the expression didn't work. It only works on the classic roads. Does anyone know how to make the expression pedal work on other channels/patches? HELP!!!!!!!!!!!!!!!