This resolution can be used if your error code start with 8007 xxxx, 8018 xxxx or C101 xxxx, try the following steps:

  1. Restart your phone, press and hold the Power button for 10 seconds.
  2. Check your internet connection, if you have a router that functions as a firewall device or if you are running firewall software on the computer, you may have to configure specific network ports 80 and 443 in the firewall so that the software can communicate correctly.
  3. You may also be able to correct this problem by using the Windows Phone Support Tool. There are two versions of the Windows Phone Support Tool available from the Microsoft Download Center. If you have a 32-bit system, download the WPSupportTool-x86.msi package; meanwhile, 64-bit users should download the WPSupportTool-amd64.msi option. (If you’re not sure whether your Windows version is 32-bit or 64-bit, go to Start, right-click Computer, select Properties and look for the System Type.)
  4. If your computer is connected to the Internet but you are still unable to update the software, make sure that the System Event Notification Service is running. To do that follow the link below, that will direct you to Support wizard.

http://gethelp.live.com is the Online Entry Point which allows users to step through the web assisted support.Select Windows Phone and then hover over the Updating your phone, and select the Solve Windows Phone Update issues. Follow the steps in the wizard.Please note that mobile browsers may have troubles to open the link. It is highly recommended to use the browser on your PC instead of your mobile browser.