Javascript error for Inserting Pages from a source

Below is a script I wrote that isn't functioning properly on my large 200 page document that I need it to. Granted there might be a much easier way to script this, but I'm no expert. I have a 200 page document that needs to be 600 pages, basically every page needs to be copied twice (and obviously placed right after the original. So I have the original PDF, then I copied that PDF to use as a source document to copy from. (To clarify if I'm not being clear, the first 3 pages would be page 1, 2, 3,... it needs to be: 1,1,1,2,2,2,3,3,3 etc)

var targetpage = 0;

var sourcepage = 0;

while(sourcepage < 199)

{

    this.insertPages({

        nPage: targetpage,

        cPath: "source.pdf",

        nStart: sourcepage,

        nEnd: sourcepage

    });

    targetpage++;

    this.insertPages({

        nPage: targetpage,

        cPath: "source.pdf",

        nStart: sourcepage,

        nEnd: sourcepage

    });;

    sourcepage++;

    targetpage=targetpage+2;

}

It gives me an error that I have no idea means, nor how to correct after only placing a total of 3 pages - so the doc went from 200 to 203 (2 of page 1 as intended, then 1 page of page 2, then for some reason it stops...

InvalidArgsError: Invalid arguments.

Doc.insertPages:9:Batch undefined:Exec

Why is it stopping? And please don't assume I know what I'm doing Thank you.