I had this plugin working fine on WordPress 3.3.1 multi site in a single server test environment, but when I moved it across to my production environment I started having problems. I am load balancing wordpress across two Linux servers but with one MySQL database server.
I network activated the plugin, then configured it site by site with my Amazon S3 details, but it seemed to work only intermittantly. By taking the servers out of the load balancing I have found that it works fine on all of my sites on one of the servers, but on the second it works for the main site but none of the sub sites.
If I upload onto this server through wordpress, at first glance it looks ok, the upload gets to 100% etc. but the files aren't getting pushed out into S3, you can't preview the images and the file location url it generates is pointing to the uploads directory for the site on my wordpress server (not my s3 bucket even though the plugin looks to be configured ok), but if you try to open the URL it returns a 404 error and the file doesn't open. So the file isn't on S3 or in my uploads/blogs.dir folder.
On the server log i can see an upload error: 'failed to open stream: Permission denied in /var/www/html/wp-admin/includes/file.php on line 348' but the permissons for my uploads and blogs.dir folders are correct for allowing uploads and uploads all worked fine before I activated the plugin!
The worst thing is if I deactivate the plugin WordPress won't return to its default behaviour of uploading just to the uploads/blogs.dir directories on the wordpress server. Uploads continue not to work even with the plgin turned off.
Does this plugin write to any files on the wordpress server, such as .htaccess that would need to be replicated on both of my load balanced servers? Although the .htaccess files on both servers do look identical!
I would appreciate any help.