I found the answer here: BeagleBone Black Google Group.
The key is to add -forever to the end of the command to start the X11vnc server.
x11vnc -bg -o %HOME/.x11vnc.log.%VNCDISPLAY -auth /var/run/gdm/auth-for-gdm*/database -display :0 - forever - nopw
I also added this command to the start up applications. System --> Preferences --> Startup Applications