missing key HKLM\Software\Policies\Microsoft\Windows\Windowsup date

In our environment we are running 3 wsus 3.0 sp1 in a 2k3 ad environment and
configure the clients using group policy and client side targeting. I'm
finding there are 20 or 30 computers out of 1000+ which are no longer
reporting into our wsus servers. I was looking in the registry and noticed
that the HKLM\Software\Policies\Microsoft\Windows\Windowsup date key is
missing. I was wondering if anyone has ever experienced this and knows what
might cause that and what the fix might be. I can search for these computers
on the wsus console and it finds them as if they had reported in at one time
but not recenlty.

the HKLM\Software\Microsoft\Windows\CurrentVersion\Win dowsUpdate\AutoUpdate
key is present and in one particlare computer I checked shows a balloon time
of 6/11/2008 a balloon type of 5 and a nextdetectiontime of 6/19. As this is
6/18 it apears as if the computer knows it needs to check in.

Was hoping someone could provide some assistance.

Thanks