Material lost when importing Obj. model


I have met a wierd problem when I try to import Obj. models to JME. I would be very much appreciated if anyone can give me a hand on that.

I have made a couple of simple models in Blender and try to import them into JME. Those models only need a color and the textures are not required.  I use totally same settings to add Materials and export the Obj. file for all the models. However, when the models were imported into JME, some of them worked well (with correct color) but the others had no color on them.

These are two examples (the first works well and the second has problem):


First One (works well)

Second One (has problem)

Many Thanks!!!!