The message means that it's not the account that the iPad's locked to - for the correct account the iPad will show in the Find iPhone section of it on http://www.icloud.com
If you can't remember the correct id (If you forgot your Apple ID - Apple Support), and if you were the original purchaser of the iPad (i.e. it wasn’t bought used), you could try going to an Apple Store (make a Genius Bar appointment if you do) or try contacting iTunes Support online (http://www.apple.com/support/itunes/ww) and see if they can remove the iPad from the account - they are likely to want to see proof of ownership before they might help e.g. original receipt with the serial number on it