Hey,

Basically laserfiche doesn't allow the use of radio buttons in lookup rules. There are some ways you can get around this tho. The easiest way is to use a dropdown rather then a radio button. If that doesn't suit your needs the next easiest way is to add a hidden text field and add JavaScript to update the value in that field whenever the radio button is changed.

The JavaScript for the second option is pretty easy but if you have trouble let me know and ill throw together a script for you.

Hope this helps.