colorbox in a view page not taking arguments

Hi,
I've created a view that loads a colorbox-node so:
<a class="colorbox-node iso-image" href="my_view_path/my_argument?width=990&amp;height=590">field_image</a>

The view that handles this path loads in the colorbox. (so when clicking the field_image the colorbox loads).

When I go directly to this page:
my_view_path/my_argument - I can see that the argument is getting applied.

However - the argument for the view is not getting applied when it's loaded in the colorbox.
I tried setting the argument to a constant, still it is never getting applied.

Any ideas why?
Thanks.