Symptoms

You have an Microsoft 365 for Home that you back up with Acronis True Image 2019 or 2020.

You have changed credentials for your Microsoft account. Since then backup is failing with:
Cannot authenticate account. Try registering your Microsoft account in the backup console again.

Solution

Re-register your Microsoft 365 in Acronis True Image:

1. In Acronis True Image 2019, click Backup, click Add backup, click the Backup source area, and then select Cloud service -> Open Online Dashboard

        

2. Sign in using the same credentials that you use to log in Acronis True Image.
3. On the sidebar, select Resources, click Add, and then choose Microsoft Microsoft 365 for Home.

        

4. Log in to your Microsoft account, when prompted.
5. If you provided credentials for the same account that was used before (e.g. you changed password), then existing backup will be continued.