Premultiply issue

[terraformers]

whats the proper way of composting 2 elements in the same scene in maya and after effects?
i want my background on a pass and my car on another, so:
-i am rendering  the background with primary visibility checked off on my car for the 1rst pass
-and a second pass with primary visibilty checked off fpr my background geometry this time
-premultiply checked off in frame buffer MR options
-i just cant the same result as my beauty pass, there is always a gray line around around my car silhouette

here are the results:
http://www.youfile.net/download.php?file=3f5a37939cbc460aaae87d54f9f9c4fe

and here is the PSD with the 2 images overlayed:
http://www.youfile.net/download.php?file=bc36b33f85bcd943e85d42e6986bf0c5

*i also tried with premultiply checked on in Maya, and for both cases i tried the 2 alpha import options in after effects, same problem.

what am i doing wrong , what is the proper workflow to obtain the exact result from the beauty pass?

[nowayfra]

Your workflow seems to be the right one and this doesnt looks like a premultiply issue, if so the grey lines would be covering your car in a more consistent way. Just try the following: In the car render pass do not set the primary visibility to off, instead set the matte opacity for your backgrund shader to zero and again render using premultiply disabled.

[terraformers]

the thing is that i am using mia_materials so i dont have the mat opacity option like maya materials.
and if i gave all the background a black lambert (with mat opacity set to 0) then the reflection will change on my car.

[nowayfra]

You can map the result of the mia_material into a maya surface shader outColor and use the matteOpacity. This maybe slows down your render a little bit.