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The message means you are meeting another part of your model when you try to pushpull that face. Try tapping the Ctrl key, to display a + sign beside the push-pull cursor. That leaves a face behind and will allow you to push-pull past the sticking point.
You’re probably running into another face or a diagonal edge.
As the guys above have said, it’s nothing special, you’ve run into an edge. Here is one way to reproduce it, and the ctrl to pass through.
thank you very much! it works!