problem with file_column url generator


I have the following in a viewer
Here, @lst = Homework.find(:all) is an array of homeworks. I checked
this this is correct.
Based on the error below, somehow, the url_for_file_colum does not
like to act on the model element.
I checked the source code to url_for_file_column, and the problem is
with instance_variable_get().
I have no idea wat is going on! Any help is appreciated. Gordon.

gordon wrote: