Unable to Update Apple TV's Software Beyond Version 5.1

I successfully updated my Apple TV to versions 5.2 using the following instructions from Apple's website...

If you have a micro USB cable (sold separately), you can restore your Apple TV from iTunes:

1. Disconnect the power and HDMI cables from Apple TV.
2. Open iTunes and verify that you are using the latest version: iTunes > Check Updates
3. Connect one end of a micro USB cable to the back of your Apple TV, and the other end to one of your computer's USB ports.
4. Apple TV (3rd generation) only: Reconnect the power cable to your Apple TV.
5. Select your Apple TV in the Source list, and then click Restore.

Your Apple TV will restore to its factory settings, and will also download and install the latest Apple TV software update. This process may take some time. Do not disconnect any cables from the Apple TV until the restore process is completed.

Details:
Apple TV version: 3rd Generation
Model number: MD199LL/A
Software Version: 5.1


Click here for a list of the Apple TV software versions

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