Why can't I install OS X 10.6.6 combined updates? To be clear, I can't install any Mac OS X update at the moment.  I reformatted my disk and installed fresh off my Snow Leopard disk.  I then continued to download 1.16GB worth of combined update (10.6.6) and I kept getting an "invalid checksum" error when attempting to open the DMG.

I'll be very clear on this to stop going around in circles.  I have spent the last 2 days looking at this issue, trawling through forum posts, re-installing, verifying and checking my disk, trying 10.6.1 instead, reformatting again, doing a zero fill, the works.  Anything that a forum seems to have suggested has not worked for me whatsoever.

Here's an output from my log:


  Mar  1 19:37:43 Kieran-Seniors-MacBook-Pro installd[182]:
  PackageKit: Install Failed: PKG: extracting "com.apple.pkg.update.os.10.6.1"
  Error Domain=PKInstallErrorDomain Code=110 UserInfo=0x10011a1e0 "An error
  occurred while extracting files from the package “MacOSXUpd10.6.1.pkg”."
  Underlying Error=(Error Domain=NSCocoaErrorDomain Code=259 "The file couldn’t be opened because it isn’t in the correct format.")
  {
  NSFilePath = "/var/folders/zz/zzzivhrRnAmviuee+++++++++++/-Tmp-/PKInstallSandbox-tmp/Root";
  NSLocalizedDescription = "An error occurred while extracting files from the package "MacOSXUpd10.6.1.pkg".";
  NSURL = "#MacOSXUpd10.6.1.pkg -- file://localhost/Volumes/Mac%20OS%20X%2010.6.1%20Update/MacOSXUpd10.6.1.pkg";
  NSUnderlyingError = "Error Domain=NSCocoaErrorDomain Code=259 \"The file couldn't be opened because it isn't in the correct format.\"";
  PKInstallPackageIdentifier = "com.apple.pkg.update.os.10.6.1";
  }
  
  Mar  1 19:37:43 Kieran-Seniors-MacBook-Pro Installer[173]: install:didFailWithError:Error Domain=PKInstallErrorDomain Code=110 UserInfo=0x1003f17f0 "An error occurred while extracting files from the package “MacOSXUpd10.6.1.pkg”." Underlying Error=(ErrorDomain=NSCocoaErrorDomain Code=259 "The file couldn’t be opened because it isn’t in the correct format.")
  
  Mar 1 19:37:44 Kieran-Seniors-MacBook-Pro Installer[173]: Install failed: The Installer encountered an error that caused the installation to fail. Contact the software manufacturer for assistance.
  
  Mar  1 19:37:44 Kieran-Seniors-MacBook-Pro Installer[173]: IFDInstallController 14EE80 state = 7
  
  Mar  1 19:37:44 Kieran-Seniors-MacBook-Pro Installer[173]: Displaying 'Install Failed' UI.
  
  Mar  1 19:37:44 Kieran-Seniors-MacBook-Pro Installer[173]: 'Install Failed' UI displayed message:'The Installer encountered an error that caused the installation to fail. Contact the software manufacturer for assistance.'.


Things I've done:


Redownloaded any update version and tried to use them.  10.6.6 was downloaded 5 times altogether with no luck.  I tried using prior versions such as 10.6.1 and 10.6.2, again with no luck.
Redownloaded from a different system.  That didn't work either.
Reformatted the disk.  That didn't do anything.  I also zero-filled.
Ran the disk repair utility


My system ran updates absolutely fine before this.  Anyone got any ideas at all?

Cheers
Sounds like some sort of silently corrupted download (I had an old router that did this occasionally).  Try a different connection using completely different modems, routers and access points.  Maybe even a different internet provider at a friend's house or office.