What happened
Paper found being sold in UP (allegedly for ~Rs 6 lakh) hours before the Sunday test; CBSE delayed the exam 2-3 hours the same morning and held a re-exam on 8/11 May 2011 for candidates unable to sit. UP STF arrested 1 and traced others. ~1.2M registered nationally; ~32,000 sat the re-exam. Day known.
What was done
Source
Primary reference icbse.com ↗ https://www.icbse.com/news/aieee-2011-question-paper-leaked-exam-postponed-elrlThis entry summarises the linked report. Where the summary and the source disagree, the source wins — and please tell us.