Using firfox I keep getting the following error when I attempt to add an item to a cart

Bad Request

Your browser sent a request that this server could not understand.
The request line contained invalid characters following the protocol string.


Apache/1.3.37 Server at www.wccomputers.com Port 80
I'm getting this in admin when working with orders as well.

Any ideas would be great. You can see it at www.wccomputers.com

Thanks