Site Backup was run, but the backup destination directory ( %1 ) is invalid. Site backup did not occur.%12 Possible cause: ...

%11Site Backup was run, but the backup destination directory ( %1 ) is invalid. Site backup did not occur.%12

Possible cause: The current site's "Backup Configuration Manager Site Server" Site Maintenance Task has invalid value set for its "Backup destination" field or
"Backup destination" exists inside the Configuration Manager root folder or
Backup was unable to create this directory.

Solution: Set a valid location to the "Backup destination" field using the Configuration Manager Console 
Make sure "Backup destination" does not exist inside the Configuration Manager root folder.
Check the privileges for proper rights%0