I will put this in the right board this time lol..
I created 2 worlds (planets) with 2 different textures and put them into 2 different folders under the assets library.
The problem is not importing them its using the models, they both seem to have the same texture applied to them so when you go to the material editor the name of the material flickers from the one it should be to "01_-_Default.material", both of the planets share the same texture that's assigned through this material and they seems to be no way of getting it to use the correct material.
you can save to another material file name but the error comes up not in resources can not save.. lol..
here is a video showing the crash and how to repeat it.