using sliders locks up XSI

[hike1]

I'm doing this tutorial:

http://www.edharriss.com/tutorials/tutorial_alpha/alpha_channel.htm

when I get to this bit, moving the sliders freezes XSI


Double click the Mix_2colors node to open it's property editor.
Check the "Multiply Weight by alpha" box and turn the RGB weight up to 1.
To help understand how the alpha interacts with the Phong material you can turn the Base color to red by moving the Red slider to 1.

http://terrymorgan.net/images/slider_lockup.jpg

So I just type in the numbers.