How do I resolve the problem of signing in to iMessage when it is saying apple ID or password is wrong while however the ID and password are valid?

I had set iMessage up on my ipad before. I stopped 3g Internet access on it for a few months. When I bounced back to continue the use access on it through wifi,i had forgotten my password. this led me to reset the password. I have been using my itunes account sine but iMessage is complaining that my ID or password is wrong.

 

I am still using the same ID though, so the problem should be the new password which is functional on iTunes.

 

I don't know why I cannot sign in to iMessage.

 

Thanks

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