cold-formed steel

Hi all, 

I'm trying to create a full-scale truss for a static loading simulation using Abaqus.
I wanted to use a Python script to do this, but I am not very experienced with this language or the Abaqus methods.

The members forming the truss are cee sections. However, at the ends of the cee sections I want to create an extruded cut

like so:
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However, when I try to use the CutExtrude command, Abaqus keeps giving me an "Invalid sketch plane" error even though I'm sure that the face I'm putting in the CutExtrude method is correct.

Hello there!

 I am fairly new to ABAQUS but I have been trying to model several experimental set-ups on cold-formed steel beams. I intend to obtain both the elastic buckling critical modes (*buckle analysis), as well as the load parameter corresponding to failure, which i first modelled through a NLGEOM analysis (*STEP, NLGEOM, INC=xxx/*STATIC, RIKS).