Packed Textures in Game Engine

Hi all

I have a student creating a project using Blender 2.55, with the Game Engine. To submit this project, she must produce a Mac and Windows version. To make life easier, I simpy wrote two scripts, one on the Mac, and one on Windows to start the file using Blender (rather than making a runtime). This works brilliantly.

The project itself was made on a Mac, and there are 3 textures, and a few objects with simple colours materials applied to them. There are 5 files in total, and each one has been saved with the materials packed into them. So far, when I have moved the project from one computer to another, all the materials appear as normal.

The problem is now when I move the project to a Windows computer, not only do the textures not appear, but none of the material colours appear. These are simple planes with a colour applied, (so in other words, there’s no nodes or mapping at all). I went back to the Mac, made sure that paths were set to relative, repacked and saved. Again on Windows, all objects default back to grey.

Am I missing something blatantly obvious here?