Acceptance to a world-class graduate school, in a highly competitive field, offers a path to credentials that open doors throughout a career, a stamp of validation to last a lifetime. Or maybe a few hours.

Carnegie Mellon University this week emailed about 800 applicants to a graduate computer science program word that they were accepted, only to email them again later the same day to say, in effect: Oops, not really. It became the latest in a string of big-name colleges to make similar mistakes. But this one had a particularly cringeworthy twist: A university renowned for its computer science offerings had fulfilled and then dashed applicants’ hopes with a computer foul-up.

That Carnegie Mellon, in Pittsburgh, had ample, exalted company in an admissions gaffe worthy of Emily Litella (the “Saturday Night Live” character who always ended her sketches with the words, “Never mind”) — including the Massachusetts Institute of Technology and Johns Hopkins University in the last year — did nothing to cushion the blow.

“It was heart-shattering,” said a 26-year-old applicant from Saudi Arabia. “The hardest part for me was telling my family and friends that congratulated me on my acceptance that I was not.”