I think this error message is coming from the web server not from php and the server is not able to find the php file to run. Or maybe php scripts are being blocked. So svManager is never getting started at all.
Some servers are picky about the permissions for scripts and their parent directory. Check what the recommended permissions are for php scripts running on your server.
Have you any .htaccess files on your server that could be limiting access to scripts?
Have any files been lost in the upload to the server?
See if you can run the phpinfo.php script which is contained in the svmtest download. That's a very simple one-line php script to list the phpinfo file.
It might be worth an email to your server support / admin.
SimpleViewer Support Team.