Recently I experienced an issue where one of my WSS 3.0 sites stopped returning search results after having worked perfectly for a long period of time. I found that the Event Log had entries stating that the Search Gatherer service was failing.
Event Type: Warning
Event Source: Windows SharePoint Services 3 Search
Event Category: Gatherer
Event ID: 2436
The first thing I tried was just to stop and start the search service and give it some time to index again. After a day or two, I returned to see that the same issue was occurring. The next step was to focus on permissions issues, but I did not understand why something that always worked would suddenly stop, since I had not made any changes to permissions on the system. The likely issue was a recent security patch on the server.
In the SharePoint Application Management back-end, I changed the account for the Search Indexer to my own login, but even my Administrator account was unable to index the site, having received the same error messages. I decided to just access the site in the browser on my web server and received an error 401.1 loading up the site. I was unaware that the search indexer even worked in this method, but apparently it was failing because it was unable to load the FQDN (fully qualified domain name) of itself using Windows Authentication.
I then was able to find a Microsoft Support Article which stated the following:
You receive error 401.1 when you browse a Web site that uses Integrated Authentication and is hosted on IIS 5.1 or a later version
This issue occurs if you install Microsoft Windows XP Service Pack 2 (SP2) or Microsoft Windows Server 2003 Service Pack 1 (SP1). Windows XP SP2 and Windows Server 2003 SP1 include a loopback check security feature that is designed to help prevent reflection attacks on your computer. Therefore, authentication fails if the FQDN or the custom host header that you use does not match the local computer name.
There are two methods listed to fix this issue. I performed both methods by editing registry settings. The first method requires a reboot of the server. I did not want to reboot the server, but after making changes specified in method 2, the search indexer began to work, so I will assume method 2 is actually what fixed the issue.
Method 2: Specify host names
To specify the host names that are mapped to the loopback address and can connect to Web sites on your computer, follow these steps:
Set the DisableStrictNameChecking registry entry to 1.
Click Start, click Run, type regedit, and then click OK.
In Registry Editor, locate and then click the following registry key:
Right-click MSV1_0, point to New, and then click Multi-String Value.
Type BackConnectionHostNames, and then press ENTER.
Right-click BackConnectionHostNames, and then click Modify.
In the Value data box, type the host name or the host names for the sites that are on the local computer, and then click OK.
Quit Registry Editor, and then restart the IISAdmin service.