Move items from old keychain to new keychain

As a workaround, you can make the password of the old keychain empty. You can do that by pressing the OK button for a second time after this error message is shown:

You can then just click the allow button repeatedly without having to type the password every time.

Keep the two files separate to start with. Use "Import Items..." from the File Menu and select your previous Keychain file. It will attempt to import all your previous keys, asking for old passwords as necessary.

When finished, all your previous data will be in the new login.keychain; your old login.keychain can be thrown away.