Cannot watch movie. Error code: 50-7

Hi. 

I cannot watch the majority of the movies I have downloaded to my sky q box on my ipad. The option is simply not available for the most, not all, of them. The option to download to ipad is available, but this is not what I want to do. 

If I click restart, next to the downloaded to sky box option. I get the error code 50-7.

This is really annoying.