Xcode iPhone "digest is missing"
Disconnect the phone/USB from your Mac and reconnected it, restarted Xcode and it worked.
I've no reason to doubt the accepted answer, but I thought I'd mention that for me the error message just went away after a while.
This may be related to iTunes finishing syncing or Aperture finishing downloading videos from my iPhone, but that's just a guess.
It could happen while incompatible MobileDevice.framework version. (it happens with beta versions Xcode most recently).
To see which version installed use command:
plutil -p /System/Library/PrivateFrameworks/MobileDevice.framework/Resources/Info.plist | grep CFBundleVersionTry to install previous (stable?) version of framework. How to install other version: here.