Abaqus - Add Constraints Function Will Not Work?!?

Hello, I'm new to this software and am running through some tutorials. I'm running into a problem where I need to add constraints to a sketch, but when I select the button nothing happens. Every other option in the sketch tools seems to work just fine except this one and I'm finding it very frustrating. I've also tried performing the same function through the "Add" menu on the toolbar with no success. Does anyone have an idea as to what I'm missing?

Abaqus ​​​​​​​