text field change value from folder level

I am pulling in data to write to a text field. However I am having difficulty just writing anything to the field. I can get the fields value. But I am getting an error when I try and change the field.

  var school=this.getField("SCHOOL NAME");

     school.value="school";

this is what I am trying but I am getting this error.

set not possible invalid or unknown.

from what I read its like I am trying to give it something that it is not. Like text to a number box. But its a text field and I am trying to give it text.

Thanks for any help.