On one PC maya models can be dragged onto the scene and render correctly.
On the other PC, the same models cannot be used at all.
Below is a composite image of the project files view from PC 1 (top) and PC 2 (bottom)
Notice how the 2d circle, hemisphere and sphere icons look different?
In order to import Maya .mb and .ma files, you need to have Maya installed on the machine you are using Unity to import the .mb/.ma file. Maya 8.0 and up is supported.