As for the KML being only for Windows, I don't believe this is the case. A KML file (Keyhole Markup Language) can be used on specific programs, most notably Google Earth and NASA World Wind, to display specific geographic data. The KML itself is OS independent, while the programs that use the KML do depend on the OS.
I've had the same problem a few times also. Always with a MAC. One time I put in a new KML and it fixed it but other times even that didn't help.