Back up has not completed recently.... but it has!

Can anyone help please?

 

I run Norton 360 v4 and get an annoying message that says "Your back up has not completed recently" even if it completed 10 minutes previously.

 

I When I click on "View Details", even this tells me that the backup was (a) successful and (b) happened a few minutes ago.

 

Am I doing something wrong or if not, is there a way of supressing this irritating warning?...