When using 2d mesh in an NX Nastran fem, I do not see plane strain (cplstn) or
plane stress (cplsts) elements as an option for element type.
In order to mesh these types of elements, the fem 2d solid option must be
defined. Use right mouse button, edit, on the name of the fem at the top of the
simulation navigator and set the 2d solid option to zx plane or xy plane.