Thousands of pupils have been unable to access their exam results via a new internet system, BBC Scotland has learned.
Almost 35,000 pupils registered to receive Scottish Higher and Standard Grades online a day earlier than usual.
The Scottish Qualifications Authority (SQA) confirmed up to 3,000 pupils had forgotten their log-on ID while others were unable to access the website.
A spokesman said they should all have their results by the end of the day.
More than a fifth of candidates have chosen to use the online service, which has been made available across Scotland for the first time.
Dozens of people awaiting results contacted the BBC Scotland news website complaining that they received an error message when trying to access the web page.
Another 120,000 will wait until Tuesday for results to be delivered by post.
The SQA said that by 1630 BST about 24,000 of the 34,683 candidates who signed up for the service, which allows candidates to view their results on a secure site, had successfully logged on to get their results.
A message on the SQA site said the system was operating as expected and advised those waiting to keep trying if it did not work at the first attempt.
About 6,000 results were sent successfully by text message.
Caitlin Leach, 17, a pupil at Broughton High School in Edinburgh, had to wait more than two hours before she was finally able to access her results.
"It was really frustrating," she said. "You spend all that time building up to get your results and then you can't get them."
Calvin McDonald, 15, a pupil at Preston Lodge High School in Prestonpans, East Lothian, received his results in a text message at 0800 BST but when he went online to double check he was unable to do so.
"The SQA knew that over 30,000 young people would be logging on this morning, and failed to take proper precautions," he said.
Michael Currie, head teacher at Our Lady's High School in Cumbernauld, said he was confident the online results system would work for all pupils in the future.
"I think the success that will come from today will ripple throughout all the pupils and next year we will get a much bigger uptake altogether."
An SQA spokesman advised candidates to be patient and keep trying if they were having difficulty accessing their results.
"There is anecdotal evidence of people having difficulty logging on," he said.
"There is no particular reason in the system why this is happening.
"The bigger difficulty is with candidates forgetting their log-on IDs."
A total of 155,893 pupils will receive their results this week, the highest ever number.
The online results service was rolled out across Scotland after being trialled for two years in Shetland, Orkney and the Western Islands.
Meanwhile, Royal Mail has said that planned industrial action will not disrupt the results.
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