Utilizing addPOSTHTTPParameter

I've added a script to run before a scrapeable, "Next", file is run called "Add Parameters".

In "Add Parameters" I've added the following line:

void scrapeableFile.addPOSTHTTPParameter("mortgage_products", "1006");

When I run the scraping session I get the following error:

Scraping file: "Next"
Next: Processing scripts before a file is scraped.
Processing script: "Freddie--Add Parameters"
ERROR--Freddie: An error occurred while processing the script: Freddie--Add Parameters
Freddie: The error message was: class bsh.ParseException (line 2): scrapeableFile .-- Encountered "scrapeableFile ." at line 2, column 14.

What am I doing wrong?