What do I do when I get "Cannot Connect to iTunes store" when downloading an app? I'm using an iPad 2, iOS 5 and trying to download apps/updates. Occasionally I get the "Cannot connect to iTunes Store" message and my downloads cancel. The iTunes store loads, all my Apple ID services work, I can view app descriptions on the App store, but when I go to download or update, I get this message.

Sometimes it's intermittent, but I've gotten it every time I tried for a week now. This also happened the day after I got my iPad; in that case I had to do a factory reset of the iPad's settings.

Resetting to factory settings (not resetting data) didn't help at all this time. However downloading updates over my phone's mobile tehering does work so it's some combination of my home wifi and iPad settings. I reset my cable modem and wireless router to no avail however. 

What else can I do to fix this?
What seems to work is signing out from my Apple ID (using the Apple ID link at the bottom of the App Store), then shutting off the device (hold the power button). Then I turn back on the device, go to the App store, enter my Apple ID info, and then try to download/update an app again. 

Just restarting or relogging in to my Apple ID alone didn't seem to be enough.