In order to get a 'normal' wah sound, first connect and calibrate an expression pedal as you normally would. Then, go into the Guitar menu of any given preset, find the Wah tab and select the Classic Wah for example. Then, on the right-hand side, the Hit Control should be set to ON. Scroll down a little and you should find that under Hi-Cut it now says Exp Pedal, and under Type, it should day Manual - if this is so, you can then tweak the Pedal Min and Pedal Max parameters to your taste, but all in all the expression pedal should now function as a 'normal' wah-wah.

Some wah pedals can act as an expression pedal, but in general, wah pedals and expression pedals are not the same.  If your wah pedal is just a wah pedal, you won't be able to use it as an expression pedal with your VoiceLive device.