Almost 1,000 students have been awarded the wrong GCSE grades in Northern Ireland.
The news came as thousands of students across the North were celebrating after the number of pupils achieving the highest grades rose again.
The main exams body, the Council for the Curriculum Examinations and Assessment (CCEA) has withdrawn results sent out for the home economics higher tier exam and warned that the vast bulk will now receive a lower mark.
Chief executive Mr Gavin Boyd said: "My staff are devastated but we realise that the people who will be most disappointed by this are the candidates themselves."
Around 800 of the 1,260 pupils involved are set to be given reduced grades.
Meanwhile the marks achieved by almost 30,000 pupils in the North showed girls outperforming boys yet again - confirming the trend set by last week's A-Levels in Britain.
About seven per cent of entries achieved the top A grade - a rise of 0.4 per cent from last year.
A total of 5.3 per cent of boys and 9 per cent of girls scored top marks.
Results are issued in Northern Ireland two days earlier than they are given out by exam boards in England and Wales because schools and colleges return for the new term earlier.
Although confirmation will only come on Thursday, it is widely expected that Northern Ireland pupils will have continued to outperform pupils in England and Wales.
The CCEA statistics also show an improvement in the A-C grade range, rising from 71.6 per cent in 2000 to 72.2 per cent this year.
PA