very strange problem:
3dsmax7 sp1/vray 1.5 (rc2/rc3) render with MASK (on some objects) - 2 files - 1.file with mask + 2.render image
insert in PS all is ok - mask over render image - OK
… close max file … open max file - RENDER - open NEW MASK FILE and insert in old PSD file (over old render image) BUT NEW MASK FILE IS’T CORRECT OVER OLD IMAGE … size…scale are differently (1%)
10x
i am not sure i understood you completely. But if i got you right you have two identical scenes, both with the same vray camera, one for masks and one for the image. And they dont match.
I assume that you tweaked the camera in the Imagefile. And the vray camera is a physical camera, so adjustments to the F-Stop change the fov slightly. so be sure to match ALL settings not just the fov.
Regards,
Thorsten
10x i find this problem
my problem:
i use vraycam but my script for generate MASK (file) using default render !!! the problem is from camera shift!!!
i will be test this problem with PSD manager comming soon comments 
The vraycam and a default cam will not line up exactly unless you move the ‘focus distance’ of the vraycam way off in the distance. You can scroll the thru the values of the focus distance and see the viewport change slightly.