File_column help: want to pass along upload info to next state via form tags

Hello.

I have a page in which I inserted the option to upload a file in a
form where other kinds of input text fields, check boxes, and radio
buttons are being filled/clicked.

I followed the steps instructed here,
http://www.kanthak.net/opensource/file_column/

except that when submitting the form, instead of saving the data
entered, I display a confirmation page, followed by a final submit
button.

It appears I lose some critical info between the first and second
pages mentioned, in that I no longer have the necessary syntax to
identify the uploaded file. I get an error when clicking submit to
get to the third page, where I get an error like:

Do not know how to handle a string with value ‘snapshot.tiff’ that was
passed to a file_column. Check if the form’s encoding has been set to
‘multipart/form-data’.

Because I merely passed along the data via hidden input tags.
Multipart/form-data is set in all forms.

-Al