Can't backup iPhone 5s (iOS 8.4) using iTunes 12.3 (because an error occured) or iCloud backup
I faced the same issue on my phone: unable to backup, neither to iCloud or through iTunes. I found some few posts, most notably this one and this one .

Basically your on the right track: backup fail because of one or more zombie app(s). Apps that were deleted but are still there...  :(

The only option seems to be to find out what app is causing this, and reinstall it, check your backup is working again, then delete it (hoping this time it will go away for good, leaving a proper state for backup to keep working ) !

To find out what is your zombie app, you'll have to find out based on whatever information you have about it. Some like me still have the app icon showing in Settings->General->Usage->Manage Storage, which make identifying pretty straight forward. Unfortunately, in your case you'll have to find out what app of 50.7MB and version 23.0 you recently deleted. To help you in your quest, you could look into:


your memory  ;)
in the App Store of your iPhone, in the list of purchased apps, look for those not installed that could match. [added base on comment below]
in iTunes, in the iPhone sync screen, app tab, the app listed as installed on your phone while you do know you removed it...
in your iTunes Library, App folder, in list view so you can sort by size
your iPhone logs, using Xcode (that's the geeky way !). see the second post listed above for a detailed how-to.


Hope you'll get to it. Good luck !

Side note: I would have added more links, but being a rookie on 'Ask Different', I'm limited to 2 external links...