After updating WordPress to version 3.1, Google Webmaster Tools found the 404 error in some of this blog posts. I discovered that problem was a dot in a permalinks. While seeking solution I found other problems with permalinks in WP 3 but none of them concerned my problem.
Finally I found the solution and I decided to describe it here. Mark Jaquith made a Periods in Titles plugin that solve this problem. I checked that it works with WP 3.1.4 and 3.2. If you are using WP 3.1 or higher check if your permalinks with dot don’t display the 404 error.