ShellExtension.dll failed to register

I am trying to install CB 2.2 on 32-bit XPpro SP3. I am getting an error which says:

Module C:\Program Files\COMODO\COMODO Backup\ShellExtension.dll
failed to register.  HRESULT -2147024891.  Contact you support
personnel.

I am running Comodo Firewall and Avast Antivirus but neither complained. I tried disabling both of them and performing a “repair” install on CB, and then uninstalling and reinstalling CB all with the same result.

The CB install executable is version 2.2.127000.12. The program seems to work despite the install error, but what will I find broken or missing? A search of the forums and with Google turned up nothing relevant. Can anyone suggest a fix?

Thanks,
George

[attachment deleted by admin]