Installation Forticlient 6.0 on MAC OS X 10.11.6 - impossible!

Hi,

I am new to this software. I would like to install FortiClient 6.0 (forticlientonlineinstaller.dmg) to my MAC OS X 10.11.6, but I constantly receive an error code: "no mountable file systems". I restarted my computer; downloaded the file with several web browsers and while google'ing my way around, I ended up here. Can someone please help me??