FS2004 Autopilot issue

[Vokial]

Thanks for the explanations about CWS but i don't really think that the King Air that comes with FS9 has it...

My problem is that the autopilot is capable to raise or lower the nose of my plane only between +500 and -500 feet/min. Example: i'm at FL300, ATC
tells my to descent to ... i don't know... FL120. I set 12.000 feet in my autopilot and then he begin the descent. The red needle on the VSI (the one
that indicates which VS you selected for the autopilot) automatically goes to the typical descent rate (approx -1300/-1500, i don't remember exactly)
and the white needle (the one that indicates the current VS of the plane) begins to fall to -1500 (or so) but then it raises to -500 and it doesn't go
further down to -1500.
On another plane for example the range of the autopilot VS was -700 / +700 but the problem is the same...
If i move the red needle, to change my desired descent rate, the white one initially falls (or climbs) to my new VS but then it returns inside that
range...

You know, that's the first time i get such a problem... really...