Flow simulation won't calculate - "No fluid volume"

Hello,

I am trying to run a flow simulation on a car I have made for my school's 'F1 in Schools challenge' team. For various reasons, I designed the car in Autodesk Inventor but I need to use solidworks to run an airflow simulation.

I tried importing the file directly from Inventor, but that resulted in gaps and geometry errors, so I experimented with a range of file types exported from Inventor. The .sat file type seemed to work pretty well as there were no errors upon import and the car seems to be made of solid bodies. I can run the flow simulation wizard perfectly, but when I try to run the actual calculation, I get an error which states:

There is no fluid volume in the project. Please check geometry or boundary conditions.

This doesn't make much sense to me, can anyone help me out?

Here's the file converted to Solidworks format:

http://dl.dropbox.com/u/41931267/Wind%20Test%202.SLDPRT

Thanks!

SolidworksFlow Simulation