Session Variable in License Agreement Screen not expanding

I am flummoxed. I have included a License Agreement Screen in my SUF9 script.

In the License Agreement Preload Action, I have this code:

Set.SessionVariable("%LicenseText%","Hello World");


Then in the Settings I select Plain Text and specify this text:
%LicenseText%

However, when I run the install, when I get to that screen, it simply shows the text:
%LicenseText%
instead of
Hello World

Am I using this the right way?

Thanks.