How To Solve "Another blog or Google Site is already using this address."

Of all of the problems that are typically reported, in Blogger Help Forum: Something Is Broken, surely the most frustrating has to be

Another blog or Google Site is already using this address.

or possibly

Key already exists for domain ...

One of the reasons for the frustration is that this is not a descriptive error - it's more of a symptom - and this symptom has a number of causes. Since many Blogger blog owners don't understand the principles of problem solving, the solutions for this error may not be obvious.

The monolithic message "Another blog or Google Site is already using this address." is actually a symptom of a number of possible problems.

Some time ago, I identified three categories of problems, which cause the message to be displayed.

1. The URL in question is actually in use, with another blog already published to that domain URL.
2. The DNS addresses are improperly setup, and not pointing to the correct Google servers.
3. There are broken / duplicate pointers, which affect the domain, in the Google internal database.

Check For A Blog Already Published To The Address

If there is a blog already published to the URL, and you control both blogs, make a simple decision - which blog to publish, to the URL in question. If necessary, a second blog can be published to a different host in the domain, and setup a domain cluster. In some cases, a previous domain owner may have published a blog, which you won't control, to the domain.

Check The DNS Address Setup

Having eliminated or solved the possibility of multiple blogs, check and - if necessary - correct the DNS addresses setup for the domain. There are three DNS address models - with one, asymmetrical, being involved with over 99% of the blogs reported with this problem. There is simply no alternative to "CNAME" referral, when publishing a blog to a custom domain.

Check For Service Redirections

With the DNS addresses corrected - and DNS propagation latency allowed for - diagnose the problem using a series of HTTP traces. Here, we'll generally see a number of possible redirections.

1. Calendar.
2. Drive and Docs.
3. Email.
4. Sites.
5. Start Page.

If the HTTP traces do not indicate a specific service, you may have an indeterminate case of database corruption.

When dealing with service redirections, start by establishing access to the Google Apps domain administrator desktop. If the domain was purchased in 2013 or later, you'll have use of a basic function Apps account. You'll use two Apps desktop wizards - "Organization & users" and "Settings".

1. Use "Organization & users", to install and activate any service.
2. Use "Settings" to disable mappings, and to uninstall any service.

Named Service Redirection

For a named service redirection:

1. If necessary, install and activate the service.
2. Delete the mappings for the service.
3. Uninstall the service.

Database Corruption Or Unknown Service Redirection

If a specific service is not identified in the HTTP traces, check the "Change URLs for multiple services" display, which is accessible from any "Change URL" service wizard.

1. Select any service, in the "Settings" wizard, and the "Change URL" link for that service.
2. Click on "Change URLs for all domain services".
3. Examine the "Change URLs for multiple services" display, and select the custom mapping, for any service with the default mapping (top) address selected. If any service entry is changed, click "Continue".
4. For each service with mapping which was just changed:
   • If necessary, install and activate the service.
   • Uninstall the service.

Just read about the details, take it one step at a time - and allow time to complete the entire task, carefully.