Zero stiffness error of a simply-supported beam

[MahmoudBrk]

Hello there,
I'm new here and this is my first post
I'm majoring in structural engineering and I need help in SAP2000.
I'm using SAP2000 Educational Version 7.10.
So I was practicing and created a simply-supported beam with a span of 6m and having uniformly distributed of 5 kN/m and concentrated load at x=3m of 10 kN/m
I assigned the frame section and material and when I did a minimized run, it gave me an error of "zero stiffness found during solution for DOF RX of joint 3 at x=6" and the structure was considered unstable and analysis was terminated.

I know my question is from the basics but I couldn't find anything related to this.

Many thanks in advance.
Regards

 

[JoshPlumSE]

If this is just a single beam that is simply supported then make sure you add in torsional restraint at one end. Otherwise a 3D program will detect an instability in that torsional direction.