This post adds to the collection of fixes for the dreaded WordPress HTTP 500 and HTTP 404 errors  users can encounter after an update . In particular, the article targets the scenerio when default Permalink settings (e.g. http://pitelspot.com/?p=123) work, but not custom structures (e.g. http://pitelspot.com/2009/04/sample-post/)  which produce HTTP404 errors. Below, I have summarize solutions that the community has offered and contributed my own fix — as I could not find it anywhere. These solutions are listed in order of frequency they were found.

COMMON FIXES FOR WORDPRESS PERMALINKS

(1) Go to http://yourdomain.com/wp-admin/options-permalink.php, click the Default  radio button, Save Changes, restart Apache, verify that post links work, then revert to you original Custom Structure (e.g.  /%year%/%monthnum%/%day%/%postname%/), Save Change, restart Apache, and hopefully it works.

(2) Delete the hidden .htaccess in your Wordpress root directory. If your folder has correct write permissions, WordPress will create a new .htaccess, otherwise it will report an error. Fixing write permission depends on you host OS .

(3) Make sure that your Apache settings file httpd.conf  has directory settings similar to

<Directory />
    Options FollowSymLinks
    AllowOverride All
    Order allow,deny
    allow from all
</Directory>

(4)  Make sure that LoadModule rewrite_module modules/mod_rewrite.so is enabled in Apache setting file httpd.conf (that was what was wrong with my server).

I hope this concise summary was useful. Please do not ask me personally what is wrong with your server as I am not an expert and there are just too many variables involved.  Feel free to discuss your issues amongst other users in the comments.