Custom HTML variables

I am trying to figure out how to pass variables from a HTML dialog window.

All I want to do is request the user to enter a file name (FileName). If I try to display the variable : %Variable%FileName% it remains empty. Seems like I am missing something really simple.

Any ideas?

Have you read:
Using Keyboard Maestro Variables in the HTML Form.

Also, you can find a lot of great examples here in the forum using the "html_prompt" tag.