I spent a couple hours this morning and came up with a solution. SFC requires access to a working cmd.exe even if run from the Sart/Run command, which I didn't have, even in safe mode. So I rebooted using F8 to get to the safe mode options and select the first Repair option above safe mode.
From there I selected Command Prompt at the bottom choice. This gave me a working cmd.exe window and I then had to run SFC /SCANNOW with the /OFFBOOTDIR=D:\ and /OFFWINDIR=D:\windows. If you don't use use these extra options it tries to run SFC on the current repair session of Windows which appears to be running on a RAM disk under X:\., which of course doen't repair anything.