403 error after upgrading to 2.5

Hi All

Upgraded last night. Seemed to all go fine and the main blog site is still viewable. I tried to follow the 2nd step in the guide

(ie. Step 2: Upgrade your installation
Visit the upgrade page. It will be at a URL like https://example.com/wordpress/wp-admin/upgrade.php. This updates your database to be compatible with the latest code, and before you do this your blog might look funny.)

but I get a 403 from that page. If I try to log into admin, I get a 403 there too. Any tips? Seems a few people on here are having similar (but not exactly the same) issues.