Answer:
A taper is a member or surface with a variable cross-section distribution. The cross-section type must be consistent; for example, I-shaped cross-sections at both member ends.
In your model, there is a member with a PRO cross-section and a QRO cross-section.
To create a tapered member here, you should use a parametric cross-section for the member start and end:
This allows you to calculate the tapered member.
