can't share whiteboard and sound at the same time

I've recently installed the new version and during my first class I had this surprise: I can't share the sound with any other screen, except the sound it self. I tried to she the sound and the whiteboard, but when I tried to check the sound box, It was gray and I wasn't able to share the sound. How can i solve this problem? I've already installed and uninstalled many times, nothing has worked. Please, i need help.