Finally got my 520 bang up to date with Denim DP.

[Smiggyy]

Finally after spending most of the weekend on it I got my trusty 520 to install 8.1 Update 1 under developer preview.
Kept getting the 0x80188308 error over and over again, would download, prepare, reboot and cogs would show for about 30/60 secs then reboot again saying it couldn't apply the update.

So I backed up phone, used the Nokia recovery tool and restored the phone to official Cyan.
Didn't set phone up, simply connected to wifi, installed the developer preview app via store, signed in and checked for updates.
This time it worked, applied all updates, reset phone again and restored backup.
Now showing as Denim.

I can only assume that it didn't like some of my installed apps while I was trying before.
All apps restored successfully afterwards.

 

[Pete]

You probably don't have Denim I'm afraid. There was a slight bug in the update where settings+info incorrectly shows Denim when it's not.

Conpare your actual firmware version with what's listed at Software update for Lumia with Windows Phone 8 - Nokia

I expect you'll see it's the same version as Cyan.

 

[Smiggyy]

Cheers fella, to be honest though I'm not bothered what version it's at as long as up to date with available updates.
I can use desktop folders and Cortana's in the house so well happy here!

OS version: 8.10.14203.306
Firmware revision number: 3058.50000.1425.0011