If you're running SharePoint, you may have come across advice to configure the DisableLoopbackCheck registry key if you're running Windows 2003 SP1 and above and/or .NET 3.5 SP1.
Adding the DWORD will certainly keep you up and running and avoid search/crawl errors like the below but it's not the way to be doing in a production environment, despite popular belief.
Access is denied. Verify that either the Default Content Access Account has access to this repository, or add a crawl rule to crawl this repository. If the repository being crawled is a SharePoint repository, verify that the account you are using has "Full Read" permissions on the SharePoint Web Application being crawled. (The item was deleted because it was either not found or the crawler was denied access to it.)
What you should be doing in production is configuring specific sites by name using the BackConnectionHostNames Multi-String Value below HKEY_LM\system\CurrentControlSet\Control\LSA\MSV1.0. The Microsoft KB article isn't clear about the format this value should take but I've found adding each site without the scheme on a new line works.
Here's an example:
Bob Fox additionally suggests adding a new DWORD named DisableStrictNameChecking with a value of 1 to HKEY_LM\system\CurrentControlSet\Services\Lanmanserver\parameters and rebooting to avoid having to reboot every time a new site is configured. I got away without rebooting at all by simply restarting the IISAdmin service.