If you are using permalinks this needs to be in your .htaccess
Code:
# BEGIN WordPress
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ - [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
</IfModule>
# END WordPress
If you re-save permalinks from the admin page, wordpress will re-write it on its own. This can also be cause by a special character in another language and stuff. I have problems with Cyrillic and despite wordpress trying to fix it, it still on their list of bugs.
If you have installed any recent plugin, try disabling them. Will not be a bad idea to give us the exact shot from the admin post page, so we can see the URL name and etc.
Regards