is this an insert page or update page?
The hidden field is only needed on the update page.
On an update page, the hidden field is used to store the name that exists in the database for that record already, so that if no file is uploaded, the default file name will use the already existing one.
on an insert page, you need only the file filed.
in the insert record behavior, bind the file column to the Wa Uploaded Files (File Field Name) -> Server File name variable.