First, thank you for your time and your advice! I've been using Solidworks for several years now, but this error has me stumped.
What the goal is:
1. Extrude a curve of an airfoil to make a wing
2. Cut-extrude through the tips of the wing at an angle to allow wingtips to be mated at an angle to create a tip dihedral in an assembly later (please see image).
I'll attach a link to a video of me trying this process and the errors I get. I've also tried creating a solid body extruded through the wing (with the "merge" option deselected) in such a way that when I use Insert -> Feature -> Combine -> Subtract I'll get the angle at the ends of the wings, but the wing tips become strange polyhedrons with a thin skin wrapped around them. I can upload a video of that too, but I'd rather do this with a good old cut-extrude method like I'm used to.
Thank you again!