Product: Microsoft Visual Studio 2005 Professional Edition - ENU -- Error 1718.File C:\WINDOWS\Installer\a4cb8.msp did not pass the digital signature check. For more information about a possible resolution for this problem, see http://go.microsoft.com/fwlink/?LinkId=73863.
I received this error when trying to install Visual Studio 2005 SP1 on a Windows Server 2003 machine.
It didn't matter whether I executed SP1 (which is over 400Mb in size) from a local or a network drive.
What ultimately fixed the problem was adding the following DWORD registry value:
PolicyScope = 1
to the following registry key:
Contrary to the a blog post, I did neither have to reboot nor have to remove the server from the domain (thankfully).
Just adding that value and re-starting the SP1 iinstallation did the trick.