Solution 1:

Already answered here: 13.10 XRDP problem with gnome-fallback

As you know by now, the ability to fire up a gnome-session with xrdp broke with Ubuntu 14.

Bug here: https://bugs.launchpad.net/ubuntu/+source/gnome-session/+bug/1251281

Ubuntu 12 does not have this problem. This might be your solution. However it will be soon out of support so that is not an acceptable option for many.

XFCE4 + tightvncserver + xrdp is an option, but you said that is not acceptible. And you may run into problems with this too. See my post here: Ubuntu 14.x with xfce4-session desktop - Terminates abruptly

I have been hanging out in #ubuntu freenode IRC chatroom looking to see if anyone has an ETA on fixing gnome + xrdp. Nothing yet.

I would suggest trying another well supported Linux distro such as CentOS6 that does not have this issue.