Unity 4.0 Mecanim Tutorial Issue

Hi all, i'm new to Unity the forums. I'm stuck on a small issue that I can't figure out. I followed this tutorial

http://video.unity3d.com/video/7362044/

No issues easy to follow along, but for some odd thereason, when I press play after I've set up my animator controller and the walk run animations along with assigning the transitions, Unity spits out a null reference error. The default idle animation works just fine. I'm not at my pc currently so sorry I don't have pics.

What I've done:
- Created an Animator controller
- assigned controller to the Animation component of my player
- setup default idle animation
- setup Locomotion branch tree with a transition coming from idle to locomotion one transition from locomotion to idle.
- set up the two float variables, direction speed. The ranges for walk run are -1 to 1.

If I can be of any other help, please don't hesitate to ask. I'd like to get my issue resolved.