I don’t like to do exactly the same blog entry that someone else did, but the other blog entry was from 2007 and I just encountered the problem myself. Thank g-d for Google.
Anyhow, if you have a web application with no site at the root managed path, adding a best bet to a site collection on some other managed path will pop up a window that says,
The search service is currently offline. Visit the Services on Server page in SharePoint Central Administration to verify whether the service is enabled. This might also be because an indexer move is in progress.
The way to fix it is to create a site collection at the root managed path. Or probably upgrade to SP1.
Yes, I know the error is completely unhelpful. I found it so as well.