“We have not been able to verify your authority to this domain. Error 13”.This is a very common error while transferring blogger address to a custom domain address. Here is some clue that will solve you problem easily.
This is not an error my friends!! You have to wait.
What is wait ?
After configuration of the CNAME (Canonical Name record) at your domain name service provider , We have to wait for time till the updated CNAME becomes effective at your DNS provider end. The time actually depends on a number of factors like DNS provider , Real time traffic etc.
This is the time could minimum at 5 minutes or max at (DNS provider dependent) , normally not more that 48 hours.
Note:- After successful update of URL(custom URL) in blogger setting Google also takes time to transfer control from blogger address to custom address (www.example.com) . This time could also ranges from 5 minute to 48 hours. normally 5 to 15 minutes.