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.
Best Answer
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.