Hi!
This error might very well be due to the fact that I am running beta software (xPlane 10.50r2), but I guess there might be a non-beta reason as well.
So, Im running xPlane beta 10.50r2 on a iMac (Catalina) purchased in 2019 (i5 3,7 GHz, radeon 580x GPU, 40GB ram). The plane I'm flying at the moment (I haven't yet tested with other planes) is the IEXG 737 payware plane. I've followed several tutorials so I believe the installation to be OK.
Problem
The sim works great when not using Swift. Also, I believe there are no problems with Swift running as long as I have not c