Rending using Mental Ray - light and shadow problems

As I was nearing the completion of my animated sequence in Maya, I wanted to test the rendered appearance of the scene so far by previewing a single frame. However my first attempt for my rendered image portrayed Moom in a luminous purple and a dark background, even though I set the specifications for the environment and plane to be white. I soon noticed that the lights were the main cause of this problem, including the shade of the camera environment which was set at a grey shade, instead of white.

The main light was set at 'illuminates by default' which created the bizarre appearance of Moom, matched with the settings of the shadows in the rendering settings. After initially finding the causes to these problems, I deleted the light and made another light, ensuring that the attributes where correct, with both the defaults and the shadows. This seemed to solved the problem, however there were no shadows on the scene.

I thought the cause of the lack of shadows could possibly be due to the floor panel being whiter than white, so to eliminate this from one of the possibilities, I changed the floor panel to just white. The white however seemed to be tinted with blue, and the shadows did slightly appear under the table. However I didnt like the appearance of the tinted blue floor panel so I went back into the material attributes and changed the hue back to whiter than whiter. I then noticed that the transparency for the floor had been increased, which I then realised was the cause of the problem, as when I rendered the scene with the transparency set to 0, the shadows were visible.