I take it you set the transparencies? You need to do the following:
1. Open GGS
2. Find the slot for Man U
3. Open the bmp in the right window
4. Press "Set Colours Opaque"
5. Test this has worked by pressing "View Alpha Mask". The whole kit should turn black. Press again to see the kit.
6. Look at the palette for this kit. There should be one neon green speck in the palette. Click on that with your pipette (arrow becomes pipette automatically over the palette).
7. Once you've selected the green speck, tick the box that says "A Only"
8. And then hit "Set Colours Transparent".
9. Tick 'All' again and then press "View Alpha Mask" again. The green parts of the kits should now be white, the rest all black.
10. Press "View Alpha Mask" to get back to the kit and drag into the first slot.
11. Repeat for away kit.