MX Simulator servers require a .trackinfo file to run.  This is not the same as uploading the .zip file or the track folder to the server.  To get a .trackinfo file for a track, you must load that track in game and type: /savetrackinfo in the game chat.  This will create a trackinfo file in the following format: yourtrackfoldername.trackinfo

That file will be in your MX Simulator personal folder.  Simply drag that file into the upload box of the server control panel.  You can then add that track to your server by clicking the "+" icon on the tracklist.