This issue is caused due to the encrypted backup through iTunes.
pop swing open the Photos app on your machine, and then trigger the Pangu app.
This should solve this issue, and you should be able to use the Cydia app.
We know it frustrates the most when the process gets stuck just when its about to complete.
Dont wrap up the Photos app afterwards and this should do it for you.
After installation, simply disconnect and reconnect your iOS machine to your rig system.
This should solve the issue.
Source :Bidness
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source: www.techworm.net