The right control key as I remember is the default key for resetting Rudder 1+2. For some reason this had never worked on my installation, and trying substituting other keys didn't work either. Searching this forum produced no previous mention of this problem. The manual doesn't mention this control specifically but mentions on p19 that you can reassign this or any key if needed.
It finally turned out that the only way to make it work on my system was to assign the same key for Reset Rudder 1, Reset Rudder 2 and Reset Rudder 1+2. (I happen to like R for this as it is easily reachable with my left hand, which also controls throttle settings), leaving Reset Mission (infrequently) to be done using the mouse.
Hope this helps someone out there.
Of course, you can also reset the rudder by double clicking it, which may be easier if you are dragging the steering wheel around with it as well.