Permission to obtain SVGDocument.getElementById property denied

Hello i am trying to make an application where i can control an SVG image from another browser window. The communication between windows is ok, and my receiver gets the info, but when i try to access to the SVG file to change something firebug tells me that i don't have permission to acess the svg file:S

to simplify, my SVG file is embebed like this:

And the way i test the access to it:

window.onload = function()
{
svgdoc = document.car1.getSVGDocument();
var door = svgdoc.getElementById("door1");
door.setAttribute("stroke-opacity",0.4);
}

What is strange is that it lets me get the SVG document... but then i can't access to the "door", wich is an element of the SVG.

Ah... and i don't have any problem with IE... it works fine there:S Can anybody help me???pleaseeeeee:)