Issue with converting .prt to .stl

I seem to be having trouble when converting this .prt file into a .stl file. When converting the file, the paddles in the middle of the wheel seem to disappear.

I'm trying to print this out using our 3D printer, I tried to find solutions like merging the sides, but it doesn't seem to work.  Does anyone know why this may be happening, and how I might go about fixing this?

I've attached the .prt file that I'm having a problem with.

Also, I'm using PTC Creo 3.0 on Windows x64

Thanks in advance for your help!