How to reassign keys in Freedom Fighters?

I only have a two button mouse, but i can't seem to reassign any key settings. Each time I go into the options menu to change key settings, the "apply" button greys out.

How to change the mousewheel for changing inventory items to some keyboard key?

Ahh it's driving me nuts!

Did you make sure you dont have two commands bound to the same key?

thx, that was the problem. Wish there was some error message that would tell you what the problem was, rather than simply greying out the apply button