Nav Data Out of Date?

I'm not sure whether this is a bug or not so I shall post any way!

Every time I start up the aircraft I now get 'NAV DATA OUT OF DATE' on the FMC. But the current AIRAC is 1313, isnt it?

Btw, my date format shown is the UK style 'dd/mm/yyyy' not the US style 'mm/dd/yyyy'

Regards

Craig