i think someone else has the same email @me.com
i get emails addressed to someone - e.g. michaelsmith@me.com whereas my email is michaelsmith@icloud.com
iPad (3rd generation) Wi-Fi, iOS 5.0.1
@me and @iCloud are the same thing.
Try going to https://appleid.apple.com/ and sign in with your @icloud.com and then sign out and try to log in with the same email but @me.com. Use the same password.
I can log into my Apple ID using 3 emails. One @me.com, one @icloud.com (both of which share the same first part) and one @yahoo.com (with a different first part.)
iCloud: About your @icloud.com, @me.com, and @mac.com email addresses - Apple Support