Recently our MOSS farm started throwing Event id 6398.
Error: Event ID: 6398 The Execute method of job definition Microsoft.Office.Server.Search.Administration.IndexingScheduleJobDefinition (GUID) threw an exception. More information is included below.
Exception from HRESULT: 0x80040D1B
As a result, I was unable to navigate to the Search Settings in the default SSP.
Cause: It turns out that I had 2 duplicate entries in the registry for the Adobe PDF file type. Check out the registry key: HKLM\Software\Microsoft\Office Server\12.0\Search\Applications\GUID\Gather\Portal_Content\Extensions\ExtensionList This will happen when you add the file type by hand in the registry and then add it as a File Type in the SSP Host web application.
Solution: I removed one of them and restarted the Windows Sharepoitn Timer job from Services.msc MMC. Make sure you do not have multiple entries in the extensionlist.
The best option is to delete the recent entries that you might have added.