This is a common issue when a blogs rewrite rules have been altered. You will notice this when you are clicking links throughout the blog, and you get a '404' error.
The fix is as follows:
Add this to the .htaccess file.
# BEGIN WordPress
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
</IfModule>
# END WordPress
