I believe the problem is most likely related to being created in the new Development Channel releases, which are incompatible with previous versions.
This is definitely a serious impediment to sharing files and macros; When I get a chance I hope to release a (freely available) release channel version that can successfully import files created in newer versions (although obviously be unable to take advantage of their new features..)
Inspired by the coastal overlay macro I created a macro to render an RGB map depending on slope and height of the terrain, which I then use in Blender to apply different detail textures for each color channel. http://www.photoniker.net/WM/RGB_map.zip
It seems though that my macro cannot be used by users with the free basic version of WM2, I used the standard edition to create my macro. Is there any known issue with compatibility (versions)?