Ok, im not sure if this is actually your problem (like b4 says it might just be cause your having to greenscreen it), but I've seen people make this mistake often enough that I should point it out.
Its very easy to end up with a black halo effect round your image because you have effectively alpha'd it twice
. Once when compositing it with your background color, and once when applying the real alpha channel too it.
Check out this example of just a simple red dot image
On the left ive got my nicely translucent red dot. This is how I want it to appear in AlamDV.
In the centre Ive put my translucent dot on a black background to make the plugin. Ive also created an alpha channel for this image based on how translucent the dot is.
Now the image on the right is what it will look like in AlamDV. Its got a nasty black border round it and doesn't look right at all. Its quite hard to explain why this happens; Go back to the middle picture and look at a pixel on the edge of the circle. The pixel is almost black so AlamDV knows it has to draw and almost black pixel on your video, AlamDV then checks the alpha channel and sees that it should be fairly transparent. So it ends up drawing a fairly transparent almost black pixel. This effect gives the transparent blackness all round the edge.
The proper way to do it is like this
On the left I've got the same translucent red dot.
In the centre Ive put my translucent red dot on the black background and made the alpha channel based on the transparency just like before. But because Ive got the transparency information now stored in my alpha channel I no longer need it on the red dot. So I've made all parts of the red dot completely opaque.
Now on the right it looks how I expect it too, and this is how it will look in alamdv.
If it helps think of it in 2 steps;
1) What color do you want the pixel to be? Forget about transparency, just think what color it should be. If the color is red make sure you have a fully red pixel on your image. If its yellow, make sure its fully yellow etc
decide how transparent you want it. If you want it semi-transparent set the alpha channel so its semi-transparent, but don't alter the color!
Take a look at the vampire dust images without the alpha information.
They look very strange, but they work because all the transparency info is in the alpha channel.
I hope that makes it a little clearer. Basically you want all the transparency information to be contained in the alpha channel not in the actual image.