Interesting problem maybe someone can shed some light on so this is what I did: 1) Backup Wordpress (thank God I did) 2) Upgrade to V3.05 -> V3.1 3) No errors during upgrade 4) No errors in error.log On logging back in /wp-admin gets 404 page in fact any admin page 404's. The site itself is fine all pages / posts show just 404 on any admin page. Googled it and tried all the usual Permalinks / Permissions / .htaccess even disabled W3 Total Cache (deleted from plugins folder) and modified .htaccess still no good. So it was back to V3.05 via the backup - After restore all well again. Anyone got any ideas on what went wrong? I'm going to post on the WP forums but as I know there are some smart people here thought I'd ask and give you all the heads up. Ohh I've installed V3.1 on a couple of other Blogs with no problem so it's a mystery.