Unity and Vuforia - Red screen

I’ve followed this tutorial and did exactly the same as in the tutorial, but when I run my game I only get a red screen. Has this happened to anyone else here? Sorry, but I can’t tell more about the problem, because I don’t know exactly what causes the red screen.

Screenshot:

EDIT:

url to tutorial:

Check the name of material you are using as background for camera. Check it´s not the same of any other one in your scene.
Move the camera to make sure you can have camera input before pointing at the target.
Also, check the console to see if there´s any problem related to camera input, maybe FPS, or resolution could be an issue.