If your Google account password has changed since the last time you signed into the computer you'll get prompted to provide the old password. This happens because Chrome OS securely encrypts all of your data, you must enter the old password now to unlock that data. If you don't know your old password, follow the steps below.

Solution:

1. Below the password field, click “I can’t remember my password” or “Forgot old password”
   
2. Then, click “Proceed anyway” This will clear the old locally cached data for the user, and re-sync new user data from the cloud