It may happen that, when trying to log in to the Avira Online Essentials via the Facebook account, the following error message will appear:
"This Facebook account is linked with another Avira Online Essentials user"
When registering to an Avira Online Essentials account any user has to use a unique email address. Alternatively, can also be used a Facebook account, which is as well associated to a unique email address.
Subsequently, any user log in to his Avira Online Essentials account with the wrong email address will fail. This will happen also at login with an otherwise assigned Facebook account.
In this case, the specified Facebook account is assigned to another Avira Online Essentials user. The fact that "username and password" do not match, the login to the Avira Online Essentials account is not possible and the error message from above is displayed.
Please, look for the proper email address and password to successfully log in to your Avira Online Essentials account.