Add the following at the bottom of the file:
... [xrdp1] name=sesman-Xvnc lib=libvnc.so username= password=ask ip=127.0.0.1 port=ask-1
Edit the /etc/pam.d/xrdp-sesman file:
Add this line at the bottom:
... session required pam_limits.so
Edit the /etc/pam.d/common-session file.
Add this line at the bottom:
... session required pam_limits.so