For example, in my recent thread concerning mouse-behavior, I never knew that virtually any mouse could replace the one which came with my iMac. Kensington, Logitech and Microsoft all work ... albeit with left and right buttons doing the same job and the scroll wheel useless.]
I don't mean to get off topic, but try it without using the Kensington software. I have always used Kensington trackballs (haven't used a mouse since the first trackball around 1985) and have never had problems.
Currently I have the almost cheapest one they make (Orbit with scroll ring) and the ring works like a hot damn. However, I am not using the Kensington software.
ryck