DarkShadow
I had the same problem too, not exactly sure what was wrong with it. I ended up doing this:
1. Created a campaign in mechassult on the xbox
2. Using the dashboard,copied the save from the HDD to the memory card
3. Connected memory card to PC
4. AR replay software should show a mechassult save
5. Copied the save to the PC
6. Opened up the save from the PC HDD (should be under where you installed ARsave)
7.Copy and overwrite the files from the hacked save.
8. Use AR to copy the new hacked save to the memory card.
Hope that works, if not give us a PM and I can try sending mine to you.