I got this error on my test server, and by following http://support.microsoft.com/kb/938219 to remove the proxy settings that are configured in Internet Explorer on the server that hosts the Shared Service Provider (SSP), and then restart the Office SharePoint Server Search service. But the error is still there. Finally, I found someone add proxy serer in Crawling -> Proxy and timeouts. By click the “Do not connect by using a proxy server”, the crawling back to work.