Nortonsecurity.exe

I suddenly cannot open an Excel file that I have opened on a monthly basis for the last three years.  I receive a message stating the file is currently open in NortonSecurity.exe and needs to be closed.  Does anyone know how to close the file within NortonSecurity.exe?

As it is, I can make a copy or Save As.  However, I cannot modify, move or rename the current file.