[help] i can't assign a rigid element to a line segment

[piglord]

Hello!
I come from Macau, China.
Recently, I read a tutorial book about abaqus.
and i do exercise by following the book step by step.

that exercise i did is the same as the example in page31 of the following pdf file

http://imechanica.org/files/l2-elements.pdf

i am so frustrated that i can't assign r2d2 element to the rigid plate
does anyone know what is going on??

i attached the cae file .

thank you!