Yeah, I did re-enstal it in the end. I just copied all my addons and missions into a different folder, and re-enstalled the main game. I guess it can't be added after you un-install it.
The problem I was facing was that in a mission, the intro would play, then it would say 'cannot load mission: missing addons 'KOLO", and then the intro would re-start. Same this happened if I pressed Escape. :-\
But, its fixed now. ;D