I was customizing a theme in the latest Wordpress version 3.3.1. I wanted to set the permalinks from an early start to date and name and I got an error message:
The requested URL /2012/01/19/bla/ was not found on this server
After googling a bit it seems like in the htaccess file the rewrite rules are the problem as they are trying to turn the URL into variables for the wp_query system. I tested it myself and the rules in the php file change once I switch to a different permalink option and I'm asked to click yes or no. Of course for the sake of SEO I wanted the date and name in my permalink, but apparently according to the post below the Search Engine Research Page will not rate the URL as it will be seen as old. So performance wise if a permalink setting it's stating with a number the wordpress system will not triggering a flag to create a rule enhancing the permalink and slowing down the URL. I haven sorted out what seems to be the problem that makes only the default setting work but in the mean time I will stick to this one for testing and after I will see what I can do to my permalinks for the website.
More about this here: http://digwp.com/2011/06/dont-use-postname/
and here: http://ottopress.com/2011/how-the-postname-permalinks-in-wordpress-3-3-work/
27 March update - solution for pretty permalinks
Finally I got my pretty permalinks up and running.
For WordPress pretty permalinks to work on the server you need to check if it's in the Apache mod_rewrite. To do this you need to open the httpd.conf file. I'm using a PC, but I guess is the same for a Mac. Go to your WAMP folder (MAMP on a Mac) . Follow this path: bin/apache/Apache2.2.17conf/httpd.conf
#LoadModule rewrite_module modules/mod_rewrite.so
With (just remove the hash)
LoadModule rewrite_module modules/mod_rewrite.so
This will enable the rewrite of the .htaccess file for pretty links in WordPress.
Now you need to restart your Apache server. If you use http://localhost/ like I do you just need to restart your localhost server.
Don't forget to switch to the new permalink and test. It should be working now.