The frames don't flicker at all. The animation runs ok, then all of a sudden the lights dim instantly, as in one frame to the next, this may last for 7 or 8 frames then all of a sudden they're back to normal. There's a few places where it also dims for only 1 frame. I looked in the graph editor for all lights and i see no keyframes in there, i guess that would be the place to look. The first thing i though was i must have animated the intensity's accidentilly but i don't see any evidence of this. I adjusted the intensities to my liking but didn't animate them.

Wow, this is a frustrating problem. what did you mean by

"Might be power shortage also on that zone?"

Thanks again for your help. Once the render is complete i'll make the movie available to show exactly what's happening.