Okay, some more little bits of information.

I've tried a few different tif textures, all make it crash when I connect the output value of the Luminance to the cutout_opacity of the Mia_Material_X.

Saving it to a different format eg. png doesn't help (for one thing it doesn't have an alpha channel) it still crashes anyway as soon as I connect it as above.

I've tried to save my file as a Maya Ascii and a Maya Binary but that didn't help either.