subassembly and cosmos motion

Hi I'm a newbie in solidworks and cosmos motion. I have a problem with subassembly: when I put a subassembly in an assembly, I can move the various parts of the assembly (using solve flexible). When I try to move a part of the subassembly using cosmos motion I can't, because the program can't drive the internal joint on the subassembly (it can only drives the joint between the whole subassembly and other parts of the assembly) Can someone help me moving subassembly parts? Thanks a lot Annoiato72