I’ve the same problem here. I use the free version 4.0.366 – amd64 on 2 Linux machines. One is running with Debian/Jessie and the other with Kubuntu 12.04. The Debian machine is my server and I connect from Kubuntu to Debian over the Internet. It connects and I get the login screen. Even the mouse pointer changes to the look of the one on the remote machine, but it takes no keyboard nor any mouse click.
I tried the configuration switch “grab the keyboard input” and “show remote cursor pointer”, but this doesn’t change anything. I also tried to disable the firewall for a test, but no change.