Black background when the ARCamera is started

I’m working on an Augmented Reality project with Unity3D(5.1.0f(64bit)) using Vuforia 5.0.5
I have downloaded the latest vuforia sdk from the Vuforia site and I have downloaded the sample project.

I have imported the Imagetarget sample into the project.

But when I runned the project ,its showing black background.
Can anybody help me solving this issue?

Click “#Scene
It is the right of the hierarchy.

The issue got fixed for me

-Tried using Unity 5.1.3(64 bit) and Vuforia 5