Not able to load/ see Target Image in Scene

Hello Experts,

I am developing my “first” application using Vuforia 6.1.17 and Unity 5.5.

I am having problems seeing/loading the “Vuforia Stones” Image Target in my scene.

I have followed everything that was mentioned in the following YouTube video (was able to do everything correctly till 9:56 in the video - including additional tips in the comments section, as the following):

           https://www.youtube.com/watch?v=HnjbTytHH6U

In your project explorer on the bottom left, navigate to Assets>Vuforia>Prefabs. In here you will see ImageTarget and ARCamera prefab files. Drag both of them to the scene. In the Hierarchy tab on the right, click on ImageTarget and set the x,y,z position to 0,0,0 on the inspector tab on the right. Also under the inspector tab, you should see Image Target Behavior (Script) section. Set Type to Predefined. Set Data Set (or Database) to "target_images" or whatever you called it when you created the database in Target Manager in Vuforia Dev Portal. Then set Image Target to "stones" or whatever you named it earlier. Now you should see the stones image on the scene. Next click on ARCamera on the Hierarchy Tab and also set the x,y,z position to 0,0,0. Then copy your Vuforia License Key from the Vuforia website and paste into the App License Key under Vuforia Behavior (Script) under Inspector tab. Next scroll down to Database Load Behavior (Script), check the Load target_images box and Activate box.

I am sure that I am missing something very subtle, but don’t know what it is. I have also searched and found that quite a few people have faced the problem, but have been able to solve it; thus, I am hopeful.

Appreciate your help.

Thanks and Regards, Ram