I agree with Liz. Basically, unless you get a letter saying "Please, never submit to us again", then a rejection simply means "we decided not to buy this story".
They might not have liked the story . . . they might have bought a story very similar to yours ten minutes before your submission arrived . . . they may have had editorial tell them "we can only have eight stories this month instead of twelve and yours was the odd one out". Unless you know the editor and he volunteers the answer, you'll never know. It's just not worth the effort to beat your head against the rejection.
Just write a new story and submit it later - and keep trying to find new places to submit the old story. What didn't work for one editor might work for another.