You cant enter the server file name in a form element because it isnt set untill the file is uploaded to the server.
you need to hand edit the insert record server behavior to use the server file name.
This is why it is not supported to use the Dreamweaver insert record behavior with digital file pro.
Also, if you look at the code, the insert record server behavior occurs before the file is uploaded.
you need to rearrange the code so that the file is uploaded before the record is inserted, then hand edit the insert record to use the server file name variable directly instead of the form element.
This isn't a supported feature, so if your not comfortable with PHP coding, you will be better off using DataAssist.