one method is to use number of frames (n) in imported movie loop as number of frames in rotation of cube.  at time 0 in carrara, the cube is 0 z-rot, at frame n it's 90, 180, ... 360 (as desired).  then the rendered movie loops, rather than trying to rotate the object svl. times in carrara.  in poser it's slightly different - render to frame n + 1 to get it to loop.