USE AT OWN RISK:
Delete dll files that are listed in 'Active Setup Log.txt', except shell32.dll
C:\WTSRV\System32\shdocvw.dll
C:\WTSRV\System32\wininet.dll
C:\WTSRV\System32\urlmon.dll
C:\WTSRV\System32\shdocvw.dll
C:\WTSRV\System32\shlwapi.dll
C:\WTSRV\System32\Wintrust.dll
C:\WTSRV\System32\digsig.dll
C:\WTSRV\System32\INSENG.DLL
C:\WTSRV\System32\JOBEXEC.DLL
export following reg key for backup purpose (then you should backed up the dll`s too):
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Active Setup
Delete following reg key:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Active Setup
Make sure Oleaut32.dll exists in Windows\System32 folder.
In the
folder, rename the following file with a .old file extension:
Active Setup Log.txt
Reinstall.
NOTE: See README file on installation CD, newest service pack and IEx distribution to check IEx installation instructions.
Further information: See http://support.microsoft.com/support/kb/articles/Q196/4/59.ASP?LN=EN-US&SD=gn&FR=0
------------- NOTE ------------
This is Microsoft official solution. This did not work for me, and rumors on the street told that the solution is to delete pagefile.sys and add it again. This worked and the reason for this seems to be that pagefile.sys may get damaged by some cause not known by Micro$oft (or else, we all would be downloading service pack X at a size of XXXMB... 
)
