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Update is non-reversible

If you use Zune or Cab-sender to update to Windows Phone 7.8 (when it becomes available), the process is non-reversible. This means that you can't use your Zune backup to restore to a version from before the update to Windows Phone 7.8. If more updates will follow, you will be able to restore to earlier versions from Windows Phone 7.8. But still not to versions earlier than that. Microsoft has decided to flag the Windows Phone 7.8 update as "not possible to restore to earlier build anymore".

In most cases, it will still be possible to do a full flash with an older stock ROM image. But that means you loose unlocks and app-data.

If you updated to Windows Phone 7.8, using Zune, and then try to restore a backup, you will get error 801812E0. Microsoft provides this information and they insure you that your device is okay, even though you get the error code.

I'm not sure why Microsoft decided to do this, but I guess this is meant to be some anti-piracy-measure.

Unlocks

If you unlocked your device using "alternative methods", I advise you to wait until the Cabs are available to use with Cab-sender and then take some precautions before updating, because reverting might not be an option. I have not actually tested this for the Windows Phone 7.8 update, but I will try to get confirmation as soon as possible.

Steps:

  • Download the necessay Cab files.
  • Make sure you have WP7 Root Tools fully installed on your phone.
  • Put your phone in Airplane mode and don't enable internet until all steps are done.
  • On PC go to %systemroot%/system32/drivers/etc and open the hosts file in a text editor and add this line:
    127.0.0.1 developerservices.windowsphone.com
  • Install the CAB files using Cab-sender.
  • Your phone should still be unlocked now. Open WP7 Root Tools, go to the Tweaks tab, and enable "Prevent relock".
  • Now you can disable Airplane mode.

I hope this will help you with the update. But remember: this method is not yet confirmed for the Windows Phone 7.8 update!

- Heathcliff74 -