"XFA template Model is empty" error

I have a process that takes an interactive form and makes it non-interactive.

It works really well for one form when I use the literal for the input to my Render PDF.

I need to be able to give the process any one of about 100 different forms and have the process work for that particular form.

I created a variable (docInputPDF) and have tried passing that to my process on the intranet, but I get the error "XFA template Model is empty.".

Since it works with a literal, but not a variable, I figure that there must be something wrong with the way that I am passing the variable.

This is the way I am passing it:

http://wpdotqvm022:8080/rest/services/Flatten_Forms/Processes/Render?F orm_Name.xdp

Any help would be greatly appreciated.

Bob Mathis