Federico Alzamora Previtali

Hello Paul, 

When does this message appear? You said during your simulation. Do you have animation for contour plots or orther displays?

This message typically appears when you select a boundary in a mesh or contour that was automatically created when you set the Mesh Interface.

If you do not set any specific options when setting the Mesh Interface, the following boundary will be created automatically.
1. When connecting fluids with the Mesh Interface
 ・Common part: interior
 ・Non-shared parts: Non-overlapping wall
2. When connecting fluids and solids, or solids and solids with the Mesh Interface
 ・Common part: Double-sided wall
 ・Non-shared part: Non-overlapping single-sided wall

Boundaries created in these intershared and non-shared parts can exist as zones and have boundary conditions. However, since there is no actual state as a mesh, if you try to display it with a mesh or contour, the above message will be displayed.
In post-processing, etc., please select the original interface plane to display instead of the automatically created boundary.