Help! wall mounted cantilever Crane Analysis with Solidworks simulation

Hi guys. I am new to Solidworks simulation. I am trying test if this crane would withstand under torsion and bending moment.
I used AISI1020 steel as the material property of the entire structure and 1500kg of load is applied at the free end. The column is fixed on top and bottom, and 50 x10 flat bars (as stiffeners) are placed between the flanges of the Uni beam.
I have tried to assign fixings and connectors but an error occurs with a pop-up saying the structure is unstable. I know I am missing something or assigning wrong fixings and connectors, but I have no idea how to fix this.