The Lumia Cyan update has only just started rolling out for the Lumia 625 and Lumia 925, but already we're seeing some of the first bugs come to light. According to a lengthy thread on the Nokia support forum, consumers are experiencing issues after upgrading their Lumia Windows Phones running the 8.1 Preview for Developers and using BitLocker full disk encryption.
The BitLocker encryption appears to cause the smartphone to hang on boot, making it unusable. All that's presented to the user is a message to connect the device to a PC. Luckily, there's a solution, but it requires a full reset the Windows Phone using Nokia's software suite.
If you update your Windows Phone on your own and have BitLocker enabled through your corporate device policies (consumer devices do not), you'll be met with the following error (image courtesy of Tom Unnérus):
To recover this drive, plug in the USB drive that has the BitLocker recovery key.
BitLocker needs your recovery key to unlock your drive because the trusted platform module is not accessible.
For more information on how to retrieve this key, go to http://windows.microsoft.com/recoverykeyfaq from another PC or mobile device.
Press Enter to Reboot and try again
Press Esc or the windows key for other recovery options"
As noted above, there is a solution to this problem, which is to completely reset the device using Nokia's software recovery suite. This should return everything back to normal. According to reports on the same thread (as well as elsewhere), those who upgrade from Windows Phone 8.0 Update 3 to Windows Phone 8.1 and Lumia Cyan have no issues.
It is important to note that regular consumer level devices are not having this problem as BitLocker is an optional security tool enabled through corporate device policies. Although this may be a headache for an IT department, it should not affect the majority of consumers. Indeed, Windows Phone Central has not been flooded with tips on this yet.
It appears to be directly affecting owners with the Preview for Developers installed, which is strange as to why users are able to run the update in the first place. Let us know if you're experiencing issues upgrading.
We are reaching out to Microsoft about this issue for further guidance and will update this article accordingly.
Source: Nokia Discussions