I set up a new blog using Wordpress. When I changed the permalink structure to custom structure, I got an error, thus none can view of the single post. Here's the error message: The requested URL /2008/10/03/name-of-my-blog-post/ was not found on this server. Additionally, a 404 Not Found error was encountered while trying to use an ErrorDocument to handle the request. Apache/2.2.9 (Unix) mod_ssl/2.2.9 OpenSSL/0.9.8b mod_auth_passthrough/2.1 mod_bwlimited/1.4 FrontPage/5.0.2.2635 PHP/5.2.6 Server at domainname.com Port 80 Tell me, please, how to fix this issue. Thank you.
You need to edit your .htaccess file. You have two choices to fix the problem. 1. CHMOD your .htaccess file to 777 and save your permalink structure again and wordpress will automatically write to it. 2. When you save your permalink structure a block of code should show up ate the bottom to add to your .htaccess file. In short all you need to do is edit you htaccess file.
I'm not sure but you can try this simple step as I explain it. Wordpress permalink structure when changed will also change your URL destination so when you change that structure, all your categories will be lost and if that happens, your URL's will surely be lost unless you change back to the original setting for your permalink structure otherwise, you can follow what Craiger 22 tipped you off.
Edit your htaccess as Craig said. If you still can't understand it, this page will be helpful. http://codex.wordpress.org/Using_Permalinks
The Permalinks Migration Plugin may also be of use to you: http://www.deanlee.cn/wordpress/permalinks-migration-plugin
Anytime, the only reason i knew how to fix it was because it happened to me when I was learning wordpress