The Error simply means you are using different Keystore (Signing file).
Check and change your Keystore file to the actual one previously used to sign this app.
Here is how to verify.
After you added your keystore, Goto TOOLS=>PRIVATE SIGN KEYS
You will see the signature (SHA1) of the keystore and make sure it matches what google is telling you, you used (F8:86:.............98:31)