Can't make clipping mask?

[Jeffery.Wright]

The top selected object must be a path, a compound shape, a text object, or a group of those.

As usual, Adobe's so called "Help" is anything but.

"Only vector objects can be clipping masks; however, any artwork can be masked." 

Well, what is a Rectangle? Not a vector? 

Why on Earth would Illustrator not let a Rectangle be used for a clipping mask? 

Why would this be active if it is not a possible operation? 

Who's idea was it to make simple operations baffling, impossible and openly hostile to users trying to get some work done? 

Why would this not be a simple and quick function? 

Can anyone at Adobe explain this philosophy? 

[Monika Gause]

You are operating inside a group there. How about isolation mode? Does that work? Exactly what are you planning to mask there?

[Ares Hovhannesyan]

Please describe what you want to do and what is your task? Thanks

[michelew83603738]

It looks like the top layer in your group may be a compoud path. Can you go into isolation mode and also explain what you are try to do so that we can better help you.