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

I've encountered an strange issue after installing RestKit with cocoapods. after resolving RestKit dependency for my project with cocoapods and trying to build it, I face this error:

The sandbox is not in sync with the Podfile.lock. Run 'pod install' or update your CocoaPods installation.

I tried running pod install, but no change.

Here are some shots:

  PODS:
  - AFNetworking (1.3.3)
  - RestKit (0.20.3):
    - RestKit/Core
  - RestKit/Core (0.20.3):
    - RestKit/CoreData
    - RestKit/Network
    - RestKit/ObjectMapping
  - RestKit/CoreData (0.20.3)
  - RestKit/Network (0.20.3):
    - AFNetworking (~> 1.3.0)
    - RestKit/ObjectMapping
    - RestKit/Support
    - SOCKit
  - RestKit/ObjectMapping (0.20.3)
  - RestKit/Search (0.20.3):
    - RestKit/CoreData
  - RestKit/Support (0.20.3):
    - TransitionKit (= 1.1.1)
  - RestKit/Testing (0.20.3)
  - SOCKit (1.1)
  - TransitionKit (1.1.1)

DEPENDENCIES:
  - RestKit (~> 0.20.0)
  - RestKit/Search (~> 0.20.0)
  - RestKit/Testing (~> 0.20.0)

SPEC CHECKSUMS:
  AFNetworking: 61fdd49e2ffe6380378df37b3b6e70630bb9dd66
  RestKit: 1f181c180105a92f11ec4f6cd7de37625e516d83
  SOCKit: 2f3bc4d07910de12dcc202815e07db68a3802581
  TransitionKit: d0e3344aac92991395d4c2e72d9c5a8ceeb12910

COCOAPODS: 0.29.0

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