Thousands of teenagers have been told - wrongly - that they have not got a university place this autumn.
Royal Mail says relatively few forms went astray
Their applications were rejected automatically - just before they began sitting their A-level exams - because the admissions service, Ucas, had not received their forms accepting the places they had been offered.
Ucas said applicants had posted the forms in April but they did not arrive at its headquarters in Cheltenham, Gloucestershire, until the end of May - when the deadline was 15 May.
It estimates that some 9,000 students might have been affected - though the Royal Mail says only just over 200 letters went astray.
Another explanation might be that Ucas did not send out reminders this year.
It is telling people not to worry but to get in touch so that their offers of university places can be reinstated.
Ucas spokeswoman Lucy Baldwin said that each year about 9,000 applicants were rejected by default because they did not confirm their university choices.
Reasons varied - they might simply have forgotten or have decided they did not want to go to university.
This year, however, the figure was about 18,000 - twice the usual number - out of the total UK applications of more than 350,700.
She said the typical response to getting a rejection letter, even though you had sent off the acceptance form, was to get in touch to ask what had gone wrong.
So far about 6,000 had done so and had had their offers confirmed.
"Quite a lot of the replies posted in April didn't arrive until the end of May," she said.
But Royal Mail spokesperson Christine Gregory said: "We have investigated and found just over 200 have been delayed in the mail."
She added: "For those people that's unacceptable and we are very sorry - but it's not more than that."
A full investigation was being carried out to find out what had happened.
Another problem this year might have been the absence of warning letters to applicants.
Last year Ucas sent out reminders of the impending 15 May deadline. But these typically crossed in the post with people's acceptances.
"That created more concern than it solved so we decided not to do that this year, so that may have been a contributing factor," Ms Baldwin said.
"If you are at all worried, phone the inquiry line - it helps if you have your applicant number to hand.
"People shouldn't worry. It can be sorted out."
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