I keep getting a warning that my email account doesn’t exist.

It’s likely that you never secured your OpenFeint account with an email address. How to check:

1. Launch an OpenFeint-enabled game on your old iPhone or iPod Touch
2. Click on the Edit Profile tab. If “Change Your Email” isn’t listed, you have not secured your account.
3. Click on “Enable Account Retrieval” and go through that process to secure your OpenFeint account.