Adding/removing Textboxes Error?

This code was working originally. Then I had made some modifications and things weren't going right so I went back to how it was originally, and now it's not working!What this does is add a file text box when you click a button & then remove it when you click on its link. I get an error though when I click the Remove link saying that its argument is invalid. I don't understand why since its the exact same line of code the Add button has except assigned to a new variable.

This is the line that's coming up with the error: var d = document.getElementById('addToDiv'); in the removeAdditionalFile function. The error message says 'Invalid Argument'.

Here's the javascript:

function addFileTextbox()
{
var a = document.getElementById('addToDiv');
var b = document.getElementById('theValue');

[code]....