Hey there - I just created your scene, see the image below. Now how I did it:
1. Reset your scene (file, reset)
2. Create text & extrude. Apply a standard material.
3. Create plane & apply a Matte/Shadow material (use default settings)
4. Create skylight. Tick Cast Shadows and set Rays per Sample to 10
5. Upload your image into the Environment Map slot (press 8 to bring up the Environment dialog)
6. Create a Target Camera and in one of your viewports enable the Camera view (press C)
7. Tick Use Environment Background and Display Background in the Viewport Background dialog (Alt B)
8. Move Camera around until it looks right
9. Render the scene (F9)
I think you probably know most of the above, but I wanted to make sure I gave you complete instructions. I'm not sure what happened to your background, but I'm guessing it had something to do with Gamma correction (this will have been fixed by resetting your scene). Hope this helped and let me know if you want me to send my test file.