From: BINTHABIT on
1. Open regedit and goto:

HKEY_LOCAL_MACHINE\Software\Microsoft\Windows NT\CurrentVersion

2. In right-side pane look for a String value "CurrentType". Change its
value to Checked and if its already set to Checked, then set it to Free and
click on OK.

3. Exit registry editor and try to install SP3 again. Now it should install
without any problem.