I uploaded a calibrated image of S Boo with good WCS, but both VSX and GCVS report no variable star found at this location.
Michael, it must have been a passing anomaly. I just typed S Boo into VSX and it brought up the star (http://www.aavso.org/vsx/index.php?view=detail.top&oid=4305).
Just to be clear, I was referring to the Varibale Stars Index and the GCVS catalogs in the catalogs dropdown in VPhot. After loading my image of S Boo, selecting either of those catalogs would report an error message that no star was found at that location.
I now just clued-in when I saw the strange orientation of the North arrow superimposed on the image in the lower right corner of VPhot. I realized that it must be a bad plate-solve. I ran a plate solve on the image and uploaded again. All is fine now. I'll have to add "check orientation of north arrow" to my VPhot Checklist for Dummies :-)