Depending on your SSH configuration it might be necessary to use absolute paths for your command to make them execute correctly.
I found that relative paths didn't work out of the box on SuSE Linux for example. Obviously the default SSH configuration does not set the PATH environment variable for clients. Since I am very lazy I did not change ssh configuration but changed the command in SSHutdown to be an absolute path to make that red button work again.
shutdown -h now
/sbin/shutdown -h now