The issue has since been resolved. If you have been unsuccessful in mapping to your custom domain during this maintenance, you may do so now. We recommend that you delete your current domain entry and re-enter it again. We will be restoring the ability to purchase a custom domain from Blogger soon.
If you continue to experience difficulty mapping your domain, please visit the Blogger Product Forum for guidance.
- These Instructions base on the new Blog Control Panel.
404 Error on Custom Domain with Blog
also see this help blog http://blogging.nitecruzr.net/2012/09/custom-domain-publishing-is-back-and.html
Step1 Click on the X This will revert to your Blogspot URL
Step2 . Go to your Settings | Basic tab.
Find the area for "Publishing," and click the link to add a custom domain.

Step 2A Click Switch to Advance Setting then Type www.yourdomainname.com click save



Step 2A Click Switch to Advance Setting then Type www.yourdomainname.com click save

Step 3. Test your www.mydomain.com it should work.
Step 3 and if you get this error Another Blog already hosted at this address go to this url for the fix
If you get another Blog already hosted at this address you might try do this go back to your Google Apps Control panel and check your Web Mapping address in your Google Apps site
If you get another Blog already hosted at this address you might try do this go back to your Google Apps Control panel and check your Web Mapping address in your Google Apps site
- Access the Site Settings screen in the Google Apps control panel
- Select the "Web Address mapping" tab
- If you see a Web Address mapping of www then delete it.
- Then Go back to your blog control panel and enter your www.domain-name.com
- Then enter the captcha then click save.
- The Test your domain for your blog.
go back to your Bloggger setting and then try changed it again. to see if it work.
If you see this error Blogs may not be hosted at naked domains
Listed on the Blogger Known issue page Blogger known issue on the nake domain
Unofficial Blogger Help Group click here
Blogger Help Forum Click here
If you Leave a comment below be sure to include your domain name and your blog spot url for faster troubleshoot.