emacsclient gets error with ALTERNATE_EDITOR on Windows 8.1

If Emacs is already running, emacsclientw.exe works fine.  (I have .txt files (for example) associated with it with the -n flag.)  However, if Emacs is not already running, emacsclient reports an error executing alternate editor ""C:\Program Files (x86)\Emacs\bin\runemacs.exe""  (The redundant quotes are in the error message from emacsclient.)

I believe that I have set ALTERNATE_EDITOR correctly in the environment variables.  Indeed, I have the following line in the output of a SET command:

ALTERNATE_EDITOR="C:\Program Files (x86)\Emacs\bin\runemacs.exe"

which emacsclient does seem to be getting correctly.  If I put that full path on the command line, it starts Emacs as it should.

This worked correctly with Windows 7, and I cannot figure out what might be wrong with my configuration under Windows 8 to cause it.

Any suggestions would be welcome.