It happened also on a subdomain but reinstalling a component caused Akeebabackup to start again and the problem went away.
HOWEVER: on the main site, the error would not go away after trying to restart ABackup 3x.
I read that I should reinstall ABackup but that I would loose my configurations.
INSTEAD, I ran the database "repair & optimize tables" tool from Admin Tools, and the problem was fixed. ABackup worked again with no error.