thank you for earlier reply. during solving a plane stress problem on grey cast iron micro. with homogenity=0.9895 , material properties E & nu (isotropic),field-displacement(inplane, intialized to cx=0 cy=0),equation-plane stress,boundary condition-Nuemann (p0=0.1,p1=500, constant profile) at solver stage an error comes that stiffness matrix is not square matrix (no. of rows not equal to no. of columns)

can you tell why this error is coming and what is the correct method for solving any plane stress problem. i.e. which boundary conditions are to be applied, which equations to be applied and how to apply them?