The Sophos Anti-Virus component fail to install. In the installation logs (C:\Windows\Temp\) you find the following error:
Action start [TIME]: LaunchConditions.
MSI (s) (D8:D8) [TIME]: Product: Sophos Anti-Virus -- You must enable rollback to continue with setup.
First seen in
Sophos Anti-Virus for Windows 2000+
This error message is referring to a Windows installer policy that is set in the registry. Sophos Anti-Virus cannot be installed until the 'DisableRollback' key is set to zero.
What To Do
The DisableRollback registry value needs to be changed to zero. For information on the value and its location in the Windows registry see: Microsoft Dev - Center: DisableRollback
Note: As advised by Microsoft: Administrators are advised to not use this policy unless it is absolutely essential.