I would like to make a contact definition between to surfaces in my model. For that I chose the contact_tied_nodes_to_surface_constrained_offset keyword. As the "SSTYP" and "MSTYP" I choose the number 4, because I created two node sets for the two surfaces. When I run the simulation there always comes an error: "Error 20211: reading contact segment data undefined node". When I choose the number 3, a contact with the part ID the simulation is good. What can I do to solve the problem? Thanks in advance.