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.
Unable to Download Application
"App Name" could not be installed at this time.
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.