I believe you have to add the line "alpha_rejection greater_equal 128" over the texture_unit line so that the code is more like this:
material whbl3
{
technique
{
pass
{
alpha_rejection greater_equal 128
texture_unit
{
texture 9cdc8b28_D.tga
filtering trilinear
}
}
}
}
If that doesn't work, I'd try changing the image file to a .png and then trying it. Hopefully this helps!