Sophos Anti-Virus for Windows: Error 25010...WaitUntilFileUnlocked

Issue
When attempting to re-install Sophos Anti-Virus for Windows, you get the following error:

Error 25010. An error occurred while running the custom action 'WaitUntilFileUnlocked'

Sophos product and version
Sophos Anti-Virus for Windows

Operating system
Windows

What to do

In Windows Services, stop the Sophos Agent.

Try to install again.

If you need more information or guidance, then please contact technical support.