I am seeing the same problem. After upgrading from F17 to F18 I can't get 2-step authentication to work for my Google account.
From "Online Accounts"
"Expired Credentials. Please log in again."
I click "Log In" button and follow Google screens and log in successfully.
However, on returning to "Online Accounts" screen the "Expired Credentials..." message is still there.
I am seeing the same problem. After upgrading from F17 to F18 I can't get 2-step authentication to work for my Google account.
From "Online Accounts"
"Expired Credentials. Please log in again."
I click "Log In" button and follow Google screens and log in successfully.
However, on returning to "Online Accounts" screen the "Expired Credentials..." message is still there.