I discovered that my blog entries could not be found in the various search engines (Google, Microsoft Bing, Yahoo), however the main blog site could be.

In the Lifetype forums (my blog software) I learned that under certain circumstances the person/bot/client/etc accessing a blog entry gets redirected through the error page (error.php), which will send a 404 Error (file not found) first and then redirect to the corresponding correct location (or at least deliver the content).

This means: everyone was able to access the blog entries here without any problem, however in the background they always showed up as non-existant to the browser/other software. Thus, the search engines didn't crawl any further and treated the links to the individual blog entries as dead links.

I changed the URL generation method from custom url to apache mod_rewrite, which basically changes all the individual urls for the blog entries, but the benefit now is that all pages appear now as existant!

So dear search engine bots, please come again and reindex the blog :)