[ESS] M-n s is undefined

[Christopher W. Ryan]

Hello. I just set up a new computer, running Windows 7 Professional 
64-bit. I installed R 3.3.1, then MikTeX 2.9, then Vince Goulet's 
version of emacs 24.5.1 with ESS. Those are all on drive C:\, a 250 Gb 
solid state drive.  My data files and documents are on drive E:\, a 
terabyte hard drive.

In emacs, when I have an .Rnw buffer open, M-n s  is met with the error 
message in the subject line.

Sweave.sty is in C:\LOCALTEXMF\Tex\latex\Sweave

which I listed as a root in MikTeX Admin.  And I refreshed the FNDB, 
both as a user and as Admin.

How can I get M-n s  (and I assume I'll have a problem with M-P as well) 
recognized as command to sweave my file?

Thanks.

--Chris