Dan, further to my last: I heard from a couple of sources today that use of a
version of mscdex prior to v2.22, the one that comes with DOS6, will also throw
an "incorrect DOS version" error message. You might want to be certain that
v2.22 is the one you're using. It should be located in your DOS directory, so
you'd have to copy it to wherever your autoexec calls for it or modify your
autoexec to direct it to your DOS directory.