Getting this message while trying to make a card in Apple's Cards app? – You're not alone.
Following a number of user complaints about the Cards application that Apple launched in 2011 no longer functioning, Apple made a post in the Support section of their Web site noting that they are discontinuing the service:
Originally Posted by Apple
Although the service is no longer available for users, the application is still available in the App Store for free via this App Store link. We’re unsure why this is the case, but Apple may soon pull the application from the App Store to prevent confusion.
Apple notes that users can still opt for making cards in iPhoto even though the Cards application service is being shut down.
Sources: Apple via 9to5Mac