Error: "The sandbox is not in sync with the Podfile.lock..." after installing RestKit with cocoapods

I was able to fix that by updating CocoaPods.

I. Project Cleanup

1. In the project navigator, select your project
2. Select your target
3. Remove all libPods*.a in Build Phases > Link Binary With Libraries

II. Update CocoaPods

1. Launch Terminal and go to your project directory.
2. Update CocoaPods using the command pod install

After many attemps I managed to fix this problem. Variable ${PODS_ROOT} was not set and I do below trick. Go to Build Phases -> Check Pods Manifest.lock and replace

diff "${PODS_ROOT}/../Podfile.lock" "${PODS_ROOT}/Manifest.lock" > /dev/null

to

diff "${SRCROOT}/Podfile.lock" "${SRCROOT}/Pods/Manifest.lock" > /dev/null

It helps me.

If you remove all pods from your target in the Podfile, e.g.

target 'myTarget' do
pod 'great-stuff', '~> 4.0'  // you deleted this last pod
end

you'll need to manually delete these builds steps from your Xcode target Build Phases:

• Check Pods Manifest.lock
• Copy Pod resources

Cocoapods (current stable version 0.37.2) does not perform this cleanup when you run pod install.