We should improve the error message for this case but you cannot assign AirBoundaries to Faces that have an Outdoors boundary condition and have them be simulate-able. AirBoundary Faces have to be between two adjacent Rooms. If you actually have a space that is open to the outdoors and is not enclosed, then you should be modeling the whole geometry of the structure as context shade instead of treating it as an enclosed Room.
thank you for your quick answer.
I oversimplified my model and made the mistake you said in the uploaded gh.
In my original file the air boundary faces were interior surfaces, double checked them with HB Faces By Type.
Never found out why it didn’t run when assigning “AirBoundaries”, but glad that it is not a bug
Have a great week!