From the D90 manual:
Auto and scene modes are only available with CPU lenses.
If these modes are selected when a
non-CPU lens is attached, the shutter release will be disabled.
Non-CPU lenses can only be used in exposure mode M, when aperture can be adjusted manually
using the lens aperture ring (in other modes, the shutter-release will be disabled).
The camera exposure meter, auto ISO sensitivity control, and variety of other features can not be used.
If non-CPU lens is used, or if Auto-area
is selected for AF- area mode as described on page 173, camera will meter center focus point.
See page 250 for compatible lenses.