Permalink issues – 404 errors and out of ideas

Hi,

I have had my blog up and running a few days now, all going smoothly until I tried to change my permalinks for SEO, as the Yoast plugin advised. I’ve selected the ‘month and name’ setting.

I have modified my /usr/share/wordpress/.htaccess file to what WordPress admin panel told me to. It still couldn’t write to it even though I resorted to 777 after it kept failing. This in turn makes me doubt whether I’m even using the right file although it’s the only one.

I have mod_rewrite installed and running with apache2, which I have triple checked with ‘a2enmod rewrite’

My .htaccess file is (as directed):

<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ - [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
</IfModule>

Whenever I go to a post now I get a 404, this is the apache log snippet:

[Tue May 07 18:48:53 2013] [error] [client 5.65.18.60] File does not exist: /var/www/wordpress/2013, referer: http://engineers-brain-dump.co.uk/

I also get:

[Tue May 07 18:48:44 2013] [error] [client 5.65.18.60] PHP Warning: constant(): Couldn’t find constant WP_CORE_UPDATE in /usr/share/wordpress/wp-admin/includes/update.php on line 33, referer: http://engineers-brain-dump.co.uk/wordpress/wp-admin/options-permalink.php

I’m pretty lost now, and it’s my first site so I’m new to wordpress. I’ve read loads of forum posts but can’t find anything I haven’t already tried. Any tips?

Cheers