Problem - Binding to Up or Down in Keyboard Shortcuts

In the parallels preferences, I am trying to bind from W to Up, and bind from S to Down. When I try to bind to Up or Down, it instead scrolls down the drop list. I have no problem binding from A to Left, and bind from D to Right, but I want to bind to Up and Down. Any way to resolve this, like a way to disable scrolling using Up and Down?

I am using Parallels 7 on a Mountain Lion OSX.