CEC in ScreenBeam sometimes does not allow an CEC-enabled LCD/LED TV to power off.

Disable the CEC feature on the TV. CEC stands for Consumer Electronics Control, and this is an HDMI feature that many TVs and peripherals have. This feature makes your devices work better together but is often disabled by default. To make things even more confusing, manufacturers often don’t call this feature “CEC”. 

Here is a list that we have found of what different manufacturers call this feature in order to disable it: 

AOC: E-link
Hitachi: HDMI-CEC 
LG: SimpLink or SIMPLINK (HDMI-CEC)
Mitsubishi: NetCommand for HDMI
Onkyo: RIHD (Remote Interactive over HDMI)
Panasonic: HDAVI Control, EZ-Sync, or VIERA Link
Philips: EasyLink
Pioneer: Kuro Link
Runco International: RuncoLink
Samsung: Anynet+
Sharp: Aquos Link
Sony: BRAVIA Sync
Toshiba: CE-Link or Regza Link
Vizio: CEC 

HDMI-CEC allows devices connected to your TV through HDMI ports to communicate back and forth with your TV. The devices can have some control over the TV, and the TV can have some control over the devices. This means you could control your Blu-ray player through your TV remote, for example. Or devices can automatically change your TV’s input when they need to do something.