I just came across this thread. It didnt have the answer I needed, but I figured it out so will post my answer. It may not work for everyone but hopefully it may help someone. I could download n install apps no problem. Then one day it wouldnt work. It said my connection was too slow. I figured out I had changed my hotmail password a few days before and not connected it (You would think microsoft would have put simply had an error that said your password is wrong!) I logged out of the app store and then logged back in using my new password. Works fine now!
Also posted on allthehighstreet.com