The sub gear is not syncro. It should change with no problem while stationary. You are not supposed to try and shift it while moving. Only the four speed syncro shifts while in motion. If it gives a problem standing still, try differend combinations. IE: clutch in or out, motor running or not, to see if there's ANY combination that works. If not, I'd get in touch with the dealer, in fact, I'd get in touch with him anyway to see what the problem is.
Pacesetter