Sorry, I'm not able to reproduce the problem you mentioned with Norton 360 Premier 21.3 on Windows 7 SP1 64-bit. Here is what I tried:
1. Right-click on System32 folder. From the context menu, select Norton 360 > Scan now. Scan completed successfully..
2. Go inside the System32 folder & select all files. Right-click on any file to get the context menu, select Norton 360 > Scan now. Scan completed successfully.
Are you trying to do the same? Or Are you trying to run scan on multiple files/folders at the same time? Do you have "Admin" rights for your Windows User Account?
Thanks!
Harry
Norton Support