According to Herman Wouk's account, Stalin was taken by surprise by Operation Barbarossa June 1941. And since his opinion was the only one that mattered in the Soviet Union the Red Army was also surprised. That was nearly a fatal mistake for Stalin personally, and was fatal for millions of Russians. So Comrade Stalin was shrewd and ruthless but he slipped up big time there.
stalin made the same mistake in dealing with evil that everyone makes: you think you can cut a deal. Hitler proved himself totally and utterly ruthless. stalin proved himself too clever by half, he figured no one could be a bigger evil genius than himself, but he was wrong. he must of thought that hitler was like the other western leaders he knew.
as far as i know the its never been proven the two actually met, although there is some rumour i believe that they did briefly.