Perhaps it's because it's not the right version of Heroes (in version 3.1, the map obviously wasn't tested), which could be causing system issues. On XP SP2 and higher (with video settings in the game usually set to High or Very High), I played through the map to the end, and several times.
Here's a page with feedback from others who successfully completed the map, along with some hints (in English): Feedback
Auto-translated
