As Prime said, it's a false positive.
No anti-virus software is perfect. Sometimes viruses get detected as clean. Sometimes clean files get detected as viruses. Most anti-virus software developers have a way of reporting wrong detections. See if Norton's quarantine has a button to submit the file to Symantec. If you provide them with your e-mail they should contact you letting you know if the file was a virus or not and if they've patched any false detection.