Unfortunately the .mmo files that Memory Map produces are not backwards compatible and can't be opened by older versions of the software. As I have version 5 of Memory Map, that is the format the .mmo files are in.

There is a way you can still view the routes however: Download the Tracklogs .trl file instead and open it with GPSU, then save it as a .gpx. This file should then hopefully be importable into your version of Memory Map.