You will need to restore your iPad, which involves erasing the data. Hopefully your latest backup was recent. See http://support.apple.com/kb/HT1212.
Locked Out, Forgot Lock or Restrictions Passcode, or Need to Restore Your Device
8. RecBoot: Easy Way to Put iPhone into Recovery Mode - if all else fails.
Forgotten Restrictions Passcode Help
If this method does not work, then you will need to fully Restore your
device as New