I can't do any Windows Updates, because the latest installer (WindowsInstaller-KB893803-v2-x86.exe) fails to install. An excerpt from the KB893803v2.log is shown at then end of this posting. The problem appears to be that access is denied when attempting to do "DoInstallation:DoRegistryUpdates".
I tried downloading the exe file & executing it outside of Windows Update, but it still failed.
I tried to do the update in safe mode with the same result.
The error code shown on the Windows Update page is 0x80070005. Searching for that error here & elsewhere has not revealed a solution that worked for me. Many of the postings seem to be for different situations which caused the same error #.

Does anyone have any ideas / workable solutions for this problem? If it would help, I can also post text from WindowsUpdate.log

Thank you.

Exceprt from KB893803v2.log follows:

30.390: Registering Uninstall Program for -> KB893803v2, KB893803v2 , 0x0
30.390: LoadFileQueues: UpdSpGetSourceFileLocation for halmacpi.dll failed: 0xe0000102
30.406: System Restore Point set.
30.437: PFE2: Not avoiding Per File Exceptions.
30.469: GetCatVersion: Failed to retrieve version information from C:\WINDOWS\system32\CatRoot\{F750E6C3-38EE-11D1-85E5-00C04FC295EE}\Tmp.0.KB893803v2_wxp.cat with error 0x57
30.734: Copied file: C:\WINDOWS\system32\msi.dll
30.781: Copied file: C:\WINDOWS\system32\msiexec.exe
30.890: Copied file: C:\WINDOWS\system32\msihnd.dll
30.984: Copied file: C:\WINDOWS\system32\msimsg.dll
31.047: Copied file: C:\WINDOWS\system32\msisip.dll
31.047: DoInstallation: Installing assemblies with source root path: c:\windows\softwaredistribution\download\ad9c4c2a779933f83b51a49a2c88838d\
31.047: Num Ticks for Copying files : 672
31.203: DoRegistryUpdates:UpdSpInstallFromInfSection Failed for MSI.Reg.Install: 0x5
31.203: DoInstallation:DoRegistryUpdates failed
31.203: Access is denied.
31.203: KB893803v2 installation did not complete.

Select 'OK' to undo the changes that have been made.
31.203: Starting process: C:\WINDOWS\$MSI31Uninstall_KB893803v2$\spuninst\spuninst.exe /~ -q -z
34.609: Software Update Rollback has completed with return code 0xbc2. This rollback requires a reboot.
34.609: KB893803v2 installation did not complete.

Problem solved. After much ado, searching & researching, I found the solution, which was quite easy to fix, once you know what to do. In my case I needed to add a "SYSTEM" group name to my registry in the HKEY_CLASSES_ROOT section (items 6A through 6F in the article at the URL listed below).

I am posting the URL containing the solution for the benefit of anyone else who encounters this particular M$ annoyance.

http://support.microsoft.com/kb/315353/en-us