If you are on Mac El Capitan, it is a known issue with Lightroom CC2015/6 version.
References article : Lightroom and El Capitan | Mac OS 10.11
If you have recently made changes or if you have done editing in Lightroom CC2015, you would not be able to access them in Lightroom 5 as the catalog cannot be downgraded.
Thank you for the reply. Yes that is what I'm worried about. I don't want to loose access to everything I've done in LR CC2015 to-date. I may have to though, I have some work coming up that I really need to tether to my computer. Almost thinking of using Aperture, really don't want to but I might have to.
YOu are making an assumption that LR 5 (or even older versions) will tether properly in El Capitan, and I don't know if that assumption is correct. I suspect that the tethering a Nikon camera will not work in any version of Lightroom in El Capitan.
Not sure who or why I can't tether, but I was tethering fine with El Capitan until I updated to LR CC 2015. I usually check the boards before I update, won't make that mistake again.