Vray Skp2SidedMtl showing as black in mirror

[DisgruntledArchitect]

Hello all:

 

I've been working on an interior view of bathroom, and have been looking in from outside using the 2sided material trick (no material assigned to rear face.) My renderings have been fine until I made another wall the same material, and now the mirror in the bathroom is reflecting both surfaces as black. I have not changed any other settings such as max depth, etc., and when I render from within the space, the walls look normal.

 

Any idea what might be happening and how I can fix it? I'm stuck as to what it might be.