After trying to change class it says item use fail anyone know why?

The free change class "vouchers" expire although after remaining a farmer until I was level 18 without changing class I was able to change to raider then back to farmer by using the ones I had earned and not used. So it may just be the first free one you get given that expires. That's how it seems to me at least

I have the same problem... I have never changed from farmer and the one that's broke is the only one I have