Impossible to say much. Since this is apparently a team project, the first thing to check would be all your networking stuff and the CC sync functions. Even if the log-in is successful, something else may still get blocked. also verify your local storage space. You may run out in the relevant folders. Beyond that there could be a million other reasons from failed hardware acceleration to some of your co-workers having screwed up the project by introducing incompatible footage types or effects, but that's really something you need to figure out on your end.