Problem with lighting and decals.

[Sabrenoose]

I have been working on a half life 2 single player map, however i have some issues with lihgting i think or the way that the lighting in my map is being compiled. I have one environment light, and i think it is causing walls in some areas to change colour funnily, and also making decals go black when they are viewed from different angles. i have a video of this in action:
www.scotthomer.co.uk/hl2_2.avi

Any ideas?
Its really bugging me!