Movies not playing on ipad

I have just installed Infuse on my ipad air and have connected to my movies stored in Plex media server libraries on my nas.
I have one library of home movies about family and another for home movies of holidays. The content of both libraries has been made the same way - from a camcorder and using various editing programs. All movies are stored as .mp4.
When I try tp play the family movies, I get “an error occurred loading this content”
I can play the holiday movies with no problems. I can play other movies, tv shows stored in other libraries with no problems.
Can anyone help with this please?