Check that you have the necessary dependencies installed:
CentOS 6 / RHEL 6
yum install tigervnc-server gnome-core yum groupinstall Desktop
CentOS 7 & 8 / RHEL 7 & 8
yum tigervnc-server gnome-core gnome-classic-session gnome-terminal / nautilus-open-terminal control-center liberation-mono-fonts metacity
Debian / Ubuntu
apt-get install vnc4server gnome-core gnome-panel gnome-settings-daemon / metacity nautilus gnome-terminal