Hmmmm, I haven't had that problem. (bet you don't want to hear that...) My system will slow down when I get more than about 10 characters in a single scene, but two should be no problem. The first thing I'd try is resetting the Carrara Preferences (Carrara>File>Reset Preferences) It's always a smart thing to do after an update. Then, before you import any characters, try selecting the Eovia software renderer instead of Open GL (found under the interactive render settings) Sometimes C is a little finicky about OpenGL depending on your video card.