Connect to a PC with Virtual machine

When I connect to a PC everyting is working. But I want to work on the Virtual machine that is on the PC. Everytime when I start the Virtual machine, I can't do anything on the PC, I have no control and the only thing I can do is watch. The only sollution to get the control back is that the user from the remote PC minimalizes the VM and than I can work again. But working on the VM isn't possible. 

I know that it was possible in the past because I did it a while ago. But maybe it's a setting or something, I looked for it but I couldn't find it.

For both PC's, I'm using Teamviewer V12.