Comment 11 for bug 30291

This is the solution to this problem (posted in the Ubuntu forums earlier today):

In the /etc/sudoers file, there is this line:
Defaults !lecture,tty_tickets,!fqdn

This should be changed to:
Defaults !lecture,tty_tickets,!fqdn,env_keep+="DISPLAY HOME XAUTHORIZATION"

This worked for me as well as several other people who posted on the forum in this thread:
http://www.ubuntuforums.org/showthread.php?t=177738