Hi Glenn,
sorry I did not understand what you meant. This is strange, because it works fine for me.
You could hard code the projection in the script itself, if it's the same every time you run the script.
Just assign a variable for projection and point to the projection file on your hard drive, instead of using getParameterAsText.
Another way of setting a default in toolbox is this: Define the projection parameter as a string and add your default in the value table field. Not very user friendly, but it might work better for you.
Thanks,
Kat