Could it be that you are using routes helper functions like Routes. in your view/template?
If so try changing import HorseRacingNationWeb.Entries.Router.Helpers to alias HorseRacingNationWeb.Entries.Router.Helpers, as: Routes in lib/horse_racing_nation_web/entries.ex
Edit: Also check out Module BpmServer.Router.Helpers is not loaded and could not be found - #3 by benwilson512
But I think that would also be resolved by aliasing as mentioned above
