i have Lumia 520 developer preview enable........
i received an update 8.10.14219.341 but whenever i try to update it........... it give error that the update is downloaded but couldn't opened..
1) Check phone's date/time
2) Check if the phone has enough memory
3) If your phone has a memory card, try removing it and see if it works
4) Post back if the above does't fix your issue