The Dons were just 90 seconds away from a potential second-round tie with AFC Wimbledon after Lewis Guy's 49th-minute strike but Darius Charles struck in the fourth minute of injury time to send the game into extra time. And after a goalless additional period, it went to penalties with Mathais Doumbe missing the vital penalty to send the League Two side through.
Robinson said: "Sometimes you get what you deserve. I'm not at all happy with our performance - that's not us, that's not how we play. We're a much better team than that but for some unknown reason it just didn't seem to click. We didn't seem to have the ability to retain the ball and move the ball quickly.
"We were missing some massive players but overall I didn't think we did enough to win the game, we didn't have much quality. They've been told in no uncertain terms that it's unacceptable. A cup run would have been nice but our goal is to get out of this league.
"It would have been unfair on Stevenage to talk about the next tie, I never have done. I always said Stevenage would be a tough ask for us to get through and it has proven the case."