Hello,
To catch the file, zip the container Folder and when you open the zipped folder, you may see the Threat file in it.
Submit the .zip folder to Symantec Security Response Team on
https://submit.symantec.com/websubmit/essential.cgi
and
http://www.threatexpert.com/submit.aspx
Note: ThreatExpert is owned by Symantec.
I would suggest you to work on the Steps provided in the Article:
What to do when you suspect that a Symantec AntiVirus product is not detecting viruses
http://www.symantec.com/docs/TECH99222
Scanning a file with a competitor's antivirus program detects a virus, but scanning with Symantec AntiVirus or Symantec Endpoint Protection does not
http://www.symantec.com/docs/TECH98929
We also offer a self-service site to analyze files, at http://www.threatexpert.com, which can give you more information on the files you submit to it.
Hope that helps!!