Orders denied

I don’t understand why some orders gets denied. Can you please have a look at this. webshop.zadelpascentrum.be (all orders denied), seems ok but denied for some reason. This interferes with our sales ofcourse, and probably don’t see those users back. When checking why denied there is no real reason to it and everything seems ok and normal.

The page I need help with: [log in to see the link]