Tutorial - How to create a world using Real-World Height data

I got houselooking things instead of green triangles, but figured it was the same thing. However, when I went to open the file in DEM it says "Not acceptable DEM". Where am I going wrong?

To elaborate, after that error I get another box:

"Access violation at address 008E7F45 in module microdem.exe. Read of address 7EF0A1DD."

:shock: