Two-factor codes within ClockOn work on a time-based system in which they only last for a limited period, the valid time for the code is based on the Google time clock.
If you are having issues it may be that the time on your PC differs slightly from the clock that Google is using with the code verification
The easiest way to correct this on your machine is to use the Authenticator add-in for Google Chrome or Mozilla Firefox then this can be corrected by using the following steps.
- Click to open the Authenticator Add-in, and then click the Cog icon as shown below
- Select the option Sync Clock with Google
Once this has been done try to enter the new code from the authenticator again.