Sixth-formers have been left struggling with a second "impossible" question in this year's A-level exams.
Students sitting an AS-level business paper were faced with a question that did not include the information needed to come up with an answer.
The AQA exam board, which set the paper, said it was "very sorry" about the error.
A business teacher from Leicestershire told BBC News online that there were concerns among students that they had wasted so much time trying to answer the question that they had not left enough time to finish the paper.
"Myself and my students are concerned as some recognised the error and left the answer blank and some spent far too long trying to figure it out and consequently ran out of time when doing the bigger mark questions towards the end of the exam," he said.
The question was worth a maximum of three marks.
An AQA spokesman said: "We are very sorry about the error in the paper. However, we do have a robust process for ensuring that none of our students will be disadvantaged as a result our mistake.
"The examiners who will be marking the paper are aware of the problem and marks will be adjusted to ensure that all students get the right grade."
The latest mistake comes just days after it was disclosed that a maths AS-level paper, sat by 6,790 pupils, contained an "impossible" question.
The question, which was worth eight marks, 11% of the paper, was impossible to solve as it was incomplete. The OCR exam board, which set the paper, promised to take the error into account when marking the exam, amid students' concerns that the mistake could affect their university places.