It means that the connection from your router to the dish network receiver is slow which cause the video download very slow. To fix it you might want to conect the receiver to router with a Ethernet cable which is the most reliable connection but if this is no possible I would suggest to download the movies first and watch the later that way you won't see that buffering message any more.
best thing to do before watching a movie on demand on Dish receiver is to allow the movie to buffer *download* all the movie. the buffering depends on your internet speed. your speed may be slow so when you watch it, you are watching the programming faster than it is buffering the movie.
let the movie download before you watch it. i periodicly scan through the movies/tv shows and download a few so i always have a selection of things to watch when i'm ready to, thus eliminating the buffering. also increasing your speed with your internet service provider helps.