Norton 360 will not allow me to delete a downloaded executable file

I downloaded StartMeeting_installer and it would not install. I tried to delete the file and I got an error message saying, The action can't be completed because the file is open in Norton Security. Close the file and try again."

Questions: 1) Why did Norton prevent the installation? How can I fix it?

2) How do I close the file when it does not show up in Task Manager? What do I have to do to delete the file?