If the content was downloaded to the system by a user who had temporarily activated it on their SEN account as a secondary PlayStation 4, other users do not have access to that content once the downloader has signed out of PlayStation Network. To access this content either ask the purchaser to sign into PlayStation Network or purchase the content on your own SEN account.
If your content has suddenly stopped working you may find that this is because the license has expired if you have not used your PlayStation 4 online for a while. To fix this problem go to [Settings] > [PlayStation Network] > [Restore License] and press (X button).
Check that the file you are trying to start has fully downloaded. Go to the game either on the content launcher or in [Library], highlight it and press OPTIONS (do not select Start). Choose [Information] from the menu on the left and check Download Status. This will show you how much of the game has downloaded compared with the total size of the file. You cannot start the game until these two numbers are the same.
Delete any game data that exists for the title you wish to download:
Go to [Library], highlight the game (or go into the folder to highlight add-on) and press ‘Options’ and then delete. To re-download the content find it in the store and select ‘Download’.