Problem with volume calculation

Hi,
I am a student of Bologna University.
In one of my exams I'm designing a building using Maya 2010. I'm very glad to realize a model of my project using Shapeways.
At the moment, I'm trying to upload my model: I divided it into 2 parts. Performing the upload of the 2 parts separately, the "volumes" are respectively 19.48 cm³ and 19.50 cm³.
Using the "combine" command in Maya to join the 2 parts and uploading in Shapeways the entire model, the volume given is very small (0.02 cm³) even if the model's dimensions are correct (Height 2.3 cm, Width 17.0 cm, Depth 22.0 cm). Moreover the cost amounts to $ 1.53!!
It seems that the value of the entire model's volume is given by the difference of the 2 single parts volume. How it is possible? Do you know where the problem is? I don't really know how to proceed.
Thank you very much for your kind help.
Cristina

What file type did you export to? I remember a discussion of Maya using mm in it's head no mater what was selected in one of the exports. Try loading as mm in shapeways to see if that gives you the numbers you're looking for.