"Unable to Download"/"Unable to Install" on iOS app update Whenever I try to update one of my apps, it downloads 79%, stops for a moment, then the progress bar resets and one of two dialog boxes appears:


  Unable to Download Item
  
  "App Name" cannot be downloaded. Please try again later.
  
  [Done]


or


  Unable to Download Application
  
  "App Name" could not be installed at this time.
  
  [Done] [Retry]


In the case of error #1, the app then returns to normal, but has not been updated. In the case of error #2, it sits at 0% and cannot be opened. Retrying simply repeats.

This does not happen with every app. Some apps simply install as expected.

I have a 4th generation iPod touch running the Evasi0n jailbreak of iOS 6.1. Rebooting does not resolve the problem, nor does launching in Safe Mode.
When this happens to me, I find it starts because a download was interrupted.

To correct, I find it easiest to use my computer to install the update, which corrects each app it updates.