ipod touch won't accept my Apple ID

I found my ipod touch which I thought I had lost. Charged it up, put in my passcode, downloaded a book and happily listened to it while I exercised. That was yesterday. Today, I put in my passcode and a screen comes up Activation lock which wants my Apple ID and password. Put them in and it says Incorrect Apple ID or Password. I used that ID and password to log into itunes. Any suggestions? I'm very frustrated with this. Thanks!