First, do not change the name of the connections file.
You should make a duplicate of the mud.php file, then change it to use the correct information for MySQL Server, username and Password and database name fr the remote server.
There are variable names used through out the application that will reference variables created in the mud.php connection file that will not exist in the server.php connection file.
as for the error you are getting, it indicates that you cannot refer to the mySQL server by the name localhost, check with your host to determine the correct name to refer to the mysql server by.