Don’t panic as it happens to best people around :), you can always get your registration number back. Remember the details which you have entered while submitting your AIEEE 2011 application form. You need these details 1) Your Name, 2) Your Father’s Name, 3) Your Mother’s Name, 4) Your DOB, 5) The type of exam you have applied (BE , B.Arch or both and 6) The mode of your AIEEE 2011 examination (online or offline).
Keep these details ready and you will get your registration number back from AIEEE website, below is the link.
For Roll Number AIEEE 2011:
You need to check on your admit card, if not download your admit card http://www.aieee.nic.in/aieee2011/aieee/Online/AdmitInput.aspx