Problem
Add Content Source page returns error: "The start address <url> already exists in this or another content source" when trying to add a new content source, even though <url> is not seen in any other content source.
Cause
A “SharePoint” content source pointing to Server name portion of the <url> was in the past created and then subsequently deleted from the content source configuration. For some unknown reason, a portion of the “SharePoint” content source has become orphaned in the registry. It is no longer is visible in the UI, but the orphaned registry entries are still seen by the Add Content Source validation logic.
Resolution
On the Index server, locate and remove the portion of the orphaned registry subtree pertaining to the previously deleted SharePoint content source. Identify the offending orphan subtree though visual inspection of the “Path” keys under the following key:
[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Office Server\12.0\Search\Applications\<SSPGUID>\Gather\Portal_Content\Sites\*]
After the orphaned keys have been removed, recycle the Office SharePoint Server Search service (osearch) on the Index server. (Note: the mentioned keys only exist on the Index server.) After it comes back you should be able to add content sources again.
Incidentally, I have found though experimentation that even if the “SharePoint” content source was not orphaned, but was still present and intact, you cannot add a “Web Site” content source which specifies as start address anywhere below/within the SharePoint content source. For example, if you create a SharePoint content source with a start address of:
http://www.sharepoint.com/sites/site1
you will not be able to add any “Web Site” content sources of the form:
http://www.sharepoint.com/* (e.g. http://www.sharepoint.com/sites/site2 or http://www.sharepoint.com/somestaticHTMLsite )
I don’t know if this is by design or a bug. If I wanted to index some static web site that I just so happened to host on the same server as SharePoint sites, I would consider this a bug. The moral of the story is you don’t seem to be able to mix “SharePoint” and “Web Site” content sources that refer to the same server url.