Could not start disk encryption: err -11976

I'm installing Symantec Desktop Encryption on a Windows 10 PC. Symantec Desktop Version 10.3.2 MP13. The installer registered with the server successfully, asks for passphrase details and then on the next screen you get a dialog box saying "Could not start disk encryption: err -11976" (see image below). Has anyone else encountered this and how to deal with it?