Symmetry in Gridgen

Vincent

After creating a block in Gridgen I want to mirror this block. When I use the "mirror blocks for export" button, the resulting file cannot be read by Fluent. If I try to mirror the block manually by copy and mirror, the resulting grid can be read by fluent, but the gridcheck fails. The mirror plane that I use is the y=0 plane. I think the problem is that the face that is supposed to be in the y=0 plane is actually not located there, but it has a very small offset (about -5*10e-10). I tried to get rid of this offset by projecting the domain onto database entities, but that did not work. How can I solve this problem?