Thanks for your answers and help.

show us the contents of your apt sources.list.d file for freeswitch and uname -a

root@freeswitch:~# cat /etc/apt/sources.list.d/freeswitch.list 
deb http://files.freeswitch.org/repo/deb/freeswitch-1.6/ jessie main

root@freeswitch:~# uname -a
Linux freeswitch 3.16.0-4-686-pae #1 SMP Debian 3.16.7-ckt20-1+deb8u3 (2016-01-17) i686 GNU/Linux

are you sure you are using 64bit?

I thought that I was running a 64bit OS, but it looks like I was wrong. As I showed above, uname -a said i686 so its 32bit. 

Sorry, for the wrong information in my first post. Looks like that I was choosing the wrong netinst-image for download after selecting 64bit OS in VirtualBox.

I just installed a new vm with arch amd64 and everything seems to be fine. The freeswitch installation just finished without any errors. 

So, thank you a lot for your help
Dominik