I just upgraded a client's database and server to version 12. Most of it is working fine excpet their website is no longer able to access the database. I'm getting the error "Unable to open file". I thought it might be because I also upgraded the server OS from leopard to Mountain Lion but remote connection to the database still works fine. I had some trouble enabling web publishing at first but that was because the webserver wasn't automatically activated when I upgraded. I know the web server is working because I can access the server's site remotely. Also, the website is hosted and not on the same server as the database. However I also read this post and thought it might be related.