Maybe overnight new updates appeared which are now pre-requisre to be
installed before SP2 can be installed. Maybe you changed something in
hardware drivers o rit booted into a different configuration since last
night.
FYI:
SP2doesn't show on Update list for people who have conflicting
soft/hardware, it's very intelligent unlike WindowsXP and won't force
updates which are known to caus eproblems for your machine it identified as
such. You might be missing prerequisites also.

Now that you FORCED SP2, you may or may not expect problems in future,
nobody knows. Microsoft doesn't take chances with your kind of setup these
days, unlike WindowsXP where updates were more or less offered to everyone
almost the same for a given Windows version.