I just upgraded my original iPad to iOS 9.1 and it now cannot connect to the App Store. No other error is given. If I go to the App Store I get a blank page. If I try to Update an app, the screen spins for a long time and eventually gives a pop up message reading "Unable to Connect to the App Store". The connectivity of the iPad is fine and I can use other networked applications such as Safari with no problem. It is only the App Store that is not working.
How can I diagnose the cause of this problem?
Update: I signed out of the App Store by going to Settings / iTunes & App Sotre / Signout. Now, when I try to sign in, the machine hangs for about two minutes and then presents a message box that says: "Cannot connect to the iTunes Store".
Best Answer
I went to a Genius Bar to fix this.
The genius said that I needed to reinstall 9.1. He said that sometimes when 9.1 is installed something gets messed up, so it needs to be installed TWICE.
Unfortunately, you can only do this from a PC or Mac desktop computer, because iOS on the iPad does not give any option to re-install an operating system you already have.
After re-installing 9.1 the App Store did indeed work on my iPad.
Note that this machine is an original iPad.
Also, another important note is that the App Store can get munged if it is accessed from a blocked network. If you trying to use the App Store from a place where there is a firewall or advanced packet filtering, like a company network, then the App Store can get blocked and this will mess it up because it will timeout and then not attempt to connect again. The App Store uses many different ports and if any of these are blocked by a firewall, it can get messed up.
To fix this:
(1) get a clean, unblocked, unfiltered connection
(2) close any open instance of the App Store by using a 4-finger swipe up
(3) start App Store again