If the issue continues after using the troubleshooting assistant, follow these steps to remove and reinstall the Apple Mobile Device Service on Mac OS X. Note that you'll need authenticate with an administrator account and password to complete these steps.
1. In the Finder, locate iTunes in the Applications folder and drag it to the Trash.
2. Move the iTunes icon to the Trash
3. Choose Go > Go to Folder.
4. Enter /System/Library/Extensions and click Go.
5. Locate the file AppleMobileDevice.kext and drag it to the Trash.
6. Choose Go > Go to Folder.
7. Enter /Library/Receipts/ and click Go.
8. Locate the file AppleMobileDeviceSupport.pkg and drag it to the Trash. If prompted, authenticate with the admin password.
9. Choose Finder > Empty Trash and restart the computer.
10. Download and install the current version of iTunes:
www.apple.com/itunes/