Double clicking a mate does not bring up the mate

Hello,

  I am trying to set a distance mate to a global variable. I have looked at this post: https://forum.solidworks.com/thread/71049 and many others like it. I make the mate first, then I accept it. I look for the mate in the feature tree and I find it. I click, I double click, I mash click a bunch, nothing ever "pops up". Every other post I've read says single or double click it to get the mate setting to "pop up".

  If I right click the mate and click "edit feature", then I go back to the same window that I had when I created the mate. This window will not allow me to enter a global variable. It says, "please enter a number greater than or equal to 0 and less than or equal to (random numbers)". I cannot get the "modify" window pictured in the post I linked to come up.

Thanks in advance.