Missing Buffer size window

Hi there,
you know normaly if I want to adjust the buffer setting, I go to ‘devices’ then ‘VST Audio Systems’ and I can change the buffer settings, but recently when going into this page I have found that the buffer setting window is missing.
It used to be there before but now is not there. Can anyone explain why this should happen. I can still change the buffer settings on my soundcard editor, but no longer in windows. I am currently experiencing pops and crackles in my sound so need to make changes to my buffer and latency settings.

Cubase 4, M audio card, Windows XP