Problem: Your google Account password has changed since the last time you signed in to this computer. Because Chrome OS securely encrypts all of your data, you must enter the old password now to unlock the data.
Solution: You don't need the old password. Just follow these steps:
Below the password field, click “I can’t remember my password” or “Forgot old password”
Then, click “Proceed anyway” This will clear the old locally cached data for the user, and re-sync new user data from the cloud