Kirk this may be a Capture NX2 issue. I downloaded a new upgrade, 2.4.0, this morning and tried a small batch of JPEGs and they showed up in Photo Mechanic like usual. Nikon in their description of changes had this "An issue that, in some rare cases, prevented display of some JPEG images has been resolved."
I'll be shooting a lot this weekend and will let you know if the problem still exists.
Thanks for your help and sorry for the trouble.