Welcome to the Apple Community.
I'd check your HDMI cable is seated correctly at each end to begin with, pull it out and put it in again, if that doesn't help...
Please tell us how are you trying to play video from the iPad, is it via AirPlay or are you using the iPad to control the Apple TV and at what point is the message displayed.
Hi Winston (love your name)'
I did reattach everything- shut everything down a couple of times to no avail. I am using airplay and everything on my iPad air comes up beautifully on the TV screen until I start to load a video. Then I get the error message.
Thanks for your help. If you have any more ideas please let me know. I'm ready to return this Apple Air!!!