I'm sure there will be some people who disagree with me on this, but I rarely use raytraced shadows for interior scenes. My advice would be to try the render again with a few of your lights set to shadow buffer instead. It also looks like you have quite a few lights coming from different directions. Maybe try turning off the shadows for some of the lights. The nice thing about C5 is that you can make as many test renders as you want without worrying about it getting stuck.