I think you need to define your contact set between the plane and the opposite face, not the face in contact with the plane. This seems counter intuitive but when Simulation creates the shell it becomes 2 dimensional and by defining the face that originally is in contact with the plane I believe it then sees it as interfering. Sorry if my explanation is not clear. I have not done this with shells all that much but I know the virutal wall works well with solid bodies.
Bumping this thread back to life.
I have a sheet metal plate that I am trying to see deformation on. For simplicity I modeled the plate as a surface to begin with. Defined a virtual wall interaction with a portion of the surface and was getting this error.
Under the settings for the virtual wall try turning on Gap Clearance and selecting "Always Ignore" seems to be running for me.
A few years late but hopefully helpful!