1. Where did you take the shot, geographically? That will determine environmental issues. I live in Florida and on a typical humid night, that's about what I'd expect for sharpness.
2. How did you focus in LV? Manually or using contrast AF? Generally I find that using contrast AF (using the remote to activate AF) is most accurate. In both cases, is it possible you moved the camera, even a tiny bit, with your hands, affecting focus before you tripped the shutter?