iMates don't appear to be working

I am watching my way through the Clawbot assembly videos in the Vex curriculum using Autodesk Pro 2017 on Windows 10 and my iMates don’t appear to work at all. I can see them (in fact, I can’t stop seeing them) but if I click on one trying to join the first 2 components of the clawbot base frame together, it doesn’t show me a circle and if I hold down the Alt key and got to the other component, nothing happens. Any idea what I am doing wrong? My parts are not as expertly alighed as they are in the movie but they are pretty close.