There are a lot of things which can cause your search index not to work. Check that the credentials for the content access accounts are correct. Also check that this account has enough rights to access and query the content you want it to index. Make sure the URL of the site is in one of your content sources, and that there are no crawl rules blocking the URL from being indexed.
All of the above are pretty well documented when you search the web for indexing problems. Today I encountered one which isn’t, or at least I couldn’t find it. One of my sites wasn’t getting indexed, and the log was only giving me the ‘there’s an error of somekind somewhere’ message. I checked ULS and noticed some remarks telling me that a view was incompatible with the browser type. This is caused by the Gantt view, which doesn’t work in all browsers. Aparantly, the search engine is sending a user-agent string which is incompatible with the Gantt view.
The reason why this was actually blocking search was that the Gantt view was used in webpart on the default.aspx page of the root site. SharePoint encountered an error on that address and that seems to cause the indexing service to ignore the entire site completely. Removing the Gantt webpart from the page fixed the error. You could try adding a rule to exclude this page, but I think that’s going to cause the search to skip the site completely. Another aproach would be to explicitely define a startpage in the search scope which doesn’t have the gantt view on it. That’s untested though.