Solar Panels

It is about time I installed my solar panel! I have had it since november, but with one thing or another I haven't managed to set them up. You will remember I bought them from the lovely Rumi at sustainable systems. At the weekend I had assistance and wired everything together in truimph. However, I screwed the waterproof on the back of the solar panel on and then realised I needed to unscrew it to put the wire in the right place (doh!). For some reason I simply can't undo the screw. I must have cross threaded it in a fit of excitement or something, but it now looks like i need to do some screw extraction! If anyone knows how, please let me know. Next time I will be more careful!