Sophos Anti-Virus for Windows 2000+: error 1920 when installing onto Vista

Issue
1920 error when installing Sophos Anti-Virus for Windows 2000+ onto a Vista computer.

Sophos product and version
Sophos Anti-Virus for Windows 2000+

Operating system
Windows Vista

What to do

Check that the Event log is accessible and that the service is running. You may find that it is not and that other system services may not be running.
This would suggest that it is a known issue with a Windows update for Vista that affects the Access Control List on the registry.

You can try to install Service Pack 1, but you may find that that will also fail or to reset the permissions on the registry using subinacl. This is best done on the advice of Microsoft.

This is not a a Sophos issue, but a Microsoft issue and you should contact Microsoft for assistance.

If the above does not apply, continue troubleshooting the issue as described in Sophos Anti-Virus for Windows 2000+: troubleshooting error 1920 during installation.