Opening a 3D File
To import a 3D drawing file interactively, the open DGN file must be 3D. To open a 3D drawing file from the system command line, the translation seed file must be 3D.
Certain IGES entities cannot be represented in 2D. Unless you are certain that the IGES file is 2D, it is recommended that the open DGN file be 3D when the IGES file is imported.