[My mesh object has missing faces! D=]

I built a mesh object in Blender.  I exported to Collada and got my .dae file.  When trying to upload, though, the object preview has missing faces.

 

I thought maybe it was just a glitch in the render so I uploaded anyway but it shows with the same missing faces when rezzed.  Is there any way to show/fix the faces or to make sure that all faces are there if I re-upload?