404 Error on Dashboard

Hi,

I have a multisite set up and I am getting a 404 error on wp-admin on all subsites. I do however have access to wp-admin on the main site and the network admin. I have checked .htaccess and wp-config and couldn't see anything out of the ordinary. I also checked the permissions on the wp-admin folder and it is set to 755. Is there anything else I have failed to check?

Thanks.