NIS 2012 not detecting a virus on my USB Pen Drive

Hi i would like to know why Norton does not detedct a virus on my USB Pen Drive, some tecnichian at the office max told me that i have 7 virus on my usb and when i scanned the pen drive norton says that theres no virus and i saw it, and can't remove it. I also installed the new version of norton 2012, but no results.

 

 

[edit: Clarified subject.]