I have trouble running maped3, more specifically, I can't run it at all. When I open it, I get a window 'Application Error' message saying: "The application failed to initialize properly (0xc0000135). Click on OK to terminate the application."

You need to install the .NET framework - (click on the hyperlink there for the section in the docs that tells you how and why) Note, this isn't needed to play verge games or even program them, just to use the map making tools.