I had this very same problem, I think it came from installing sp1.
to remedy this I booted from my vista disk let it load as normal and
when it came to the point of install or repair click repair, then you
see the option to system restore click on that, select your restore
point, and wait until it finishes, in my case it said it was
unsuccessful but nevertheless when I rebooted it was all as it was
before and I could access updates and system restore, if you have a disk
do try it and good luck in your search.
sach
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sach
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