Thousands of university applications are thought to have been delayed by a glitch in a new computer system.
Ucas said the delays were only short-term
Many second-choice institutions were not told straight away when students failed to get the A-level or Scottish Higher grades for their first choice.
Caryl Thompson, head of admissions at Nottingham University, said this had created a "lot of extra work".
But the Universities and Colleges Admissions Service said delays had been "slight" and had had little effect.
Ucas has replaced its computer system this year and is aiming towards all applications taking place online.
Details of students who fail to get the grades demanded by first-choice universities are supposed to be forwarded to their second-choice, or "insurance", institutions the same day.
Ms Thompson said this had not happened, affecting at least 47 applicants who had listed Nottingham as one of their choices.
The students had had to get in touch themselves, she added.
Ms Thompson said: "The number for us is quite small, as we are mostly a first choice destination, but it suggests thousands of students nationally are being affected.
"The problems with the changes have created a lot of extra work for students and admissions staff.
"We have got 5,500 students coming here in the autumn and they have to get on with sorting out registration, accommodation and other issues, and this does not help."
'Not crystal clear'
Bath University also reported problems with the system.
Leslie Currie, from the admissions office, said: "We are wondering how much of a problem this has been, at a time of year when we would have hoped the information would be crystal clear."
Kingston University said it had had to contact a "handful" of students and was working to resolve any problems.
But Ucas said the glitch, which affected the new computer system and an older one still used by some institutions, had been minor.
A spokesman said some first-choice universities had electronically sent through details of student rejections after 6pm.
Because of the way the two systems worked, this meant the information was not forwarded by Ucas to the second choice for two days.
The Ucas spokesman said: "Most students won't have been aware of a problem.
"It may have caused slight delays with arranging accommodation, but universities do not normally send these details out straight away anyway."