I can't download program Pages ver 5.1 . It stops to download and tell me to download via purchase(still not working)

Depending where you are, there can be slow downs on the servers.

You just have to keep trying. I tried 3 times to get the Mavericks upfrade and eventually had to go to the Apple Store.

Where they gave me a copy of the previous version! 😁

"Eventually it works" - the new Apple slogan.

Peter