How can I add a Drawing Markup/Annotation to my stamp while it's being stamped?

Question

I have created Dynamic Stamp and works perfect and its located in my user profile:
C:\Users\XXXXX\AppData\Roaming\Adobe\Acrobat\10.0\Stamps\symbols.php
And this works just fine...
Now I want to add a line to the stamp.
I want the user to introduce the length of the line using a response box (app.response)
For some reason when I try to add the line using:
var new_line = this.addAnnot({
  type:"Line",
  page:6,
  points:[[36,373],[613,373]],
  width:2, 
  style:"S ",
  strokeColor:color.black,
  arrowEnd:"None",
  arrowBegin:"None"
After this, the variable "new_line" is NULL, can somebody help me here?
So I cant add the line using JavaScript
Ironically when I try to create a field (text box) using JavaScript it works perfectly ....
var oField=this.addField({
cName: "info",
cFieldType: "text",
nPageNum: 6,
oCoords: [ 20, 20, 1, 1 ]
oField.value = "Hello World !!!";
I am able to insert the line manually when I open the stamp file in Acrobat and add the line under Comment->Drawing Markups->Draw Line. However I want the length of the line to be inserted by the user when the user applies the stamp... Can anybody help me here?

Answer 1

I added 4 annotations to the stamps (2 Lines, 1 Circle and 1 text box)
Then I tried to get the Annotation properties and still no good luck.
The variable is NULL
I used this script:
var aAnnots = this.getAnnots(6);
app.alert("There are: " + aAnnots.length + " annots");
Note: The scrip is in the "calculate" section of one of the field text of the stamp (Custom Calculation script)
Do you want me to send the stamp?