Comment 33 for bug 1117292

Actually I understood what was wrong in my installation!!!
Basically I was reusing the same usb stick I used for a previous Ubuntu installation and the "Startup Disk Creator" application didn't cleared out the usb stick.. so files of two Ubuntu version (14.04 Desktop and Server) were coexisting causing this problem.

Chris' workaround actually worked but in the end I had a server installation with gnome, cups, xorg and other desktop packages.. :( installation was compromised.

SOLUTION:
I used dd instead of "Startup Disk Creator" (never trust GUI tools :P)
dd if=image.iso of=/dev/xxx bs=4M