Assigned Item Tax Group Not working

Hey,

Our company usually uses customer tax groups, however we have had to set up a few item tax groups, and these have been applied to the items.

However when the item is being use on the sales orders, no tax is pulling through for the item. (customer card has a default tax group assigned) 

Have we set up the item tax group incorrectly? or can the item & customer price groups not work together?

Thanks 

Mel