Have a MOSS farm the a web front-end and a separate search indexer. After installing some patches the indexer started failing with an Access is Denied message. MOSS configures a dedicated index machine by adding an entry to the HOSTS file that points the MOSS sites to the indexer’s IP address. If you try to connect to your MOSS site on the Indexer’s desktop you will unable to connect.
The patches are KB960803 and KB963027. You can read the notes here.
Following the instructions for Method 1 in the article fixed the problem and indexer was able to access and index the content again. The fix is a small registry entry that allows local connections to other host names.