I'm not quite sure what I did, but with the Transparency > Alpha: at 0.6, like Img 1, I was able to produce Img 2.

Img 1:

Img 2:

I used Img 3's node setup and it started working. Suddenly, I could see the checker background behind the cube.

Img 3:

Here is the .blend file:

http://blend-exchange.giantcowfilms.com/embedImage.png?bid=1497

Edit:

Checker Background:

I'm not quite sure what I did, but with the Transparency > Alpha: at 0.6, like Img 1, I was able to produce Img 2.

Img 1:

Img 2:

I used Img 3's node setup and it started working. Suddenly, I could see the checker background behind the cube.

Img 3:

Here is the .blend file:

Edit:

Checker Background:

I'm not quite sure what I did, but with the Transparency > Alpha: at 0.6, like Img 1, I was able to produce Img 2.

Img 1:

Img 2:

I used Img 3's node setup and it started working. Suddenly, I could see the checker background behind the cube.

Img 3:

Here is the .blend file:

http://blend-exchange.giantcowfilms.com/embedImage.png?bid=1497

I'm not quite sure what I did, but with the Transparency > Alpha: at 0.6, like Img 1, I was able to produce Img 2.

Img 1:

Img 2:

I used Img 3's node setup and it started working. Suddenly, I could see the checker background behind the cube.

Img 3:

Here is the .blend file:

http://blend-exchange.giantcowfilms.com/embedImage.png?bid=1497

Edit:

Checker Background: