create cut and fill volumes won't give me a volume

I have 2 terrain models I am trying to use the "create cut and fill volumes" tool on.  The tool creates an element, but I can not get the volume from it.  When I try and measure it, it says "cannot measure volume of this element"  I have attached the file with the 2 terrain models.  Can someone let me know why this doesn't work and if there is a way to fix it?

thankstupper trial.dgn