Actually, technically I think I was just stupid about it-- I have the range of motion easily, but maybe not the strength to support it. I've been doing it for 2 weeks, noticed knee pain after the first, but after the 2nd week (doing it both M and F) I can't go up stairs without pain (behind patella mainly).
So I'm resting my legs until I can bear weight on them without wincing. And quite honestly, nervous to get back to inside squats.
If this happens, do you skip? Carry on very carefully? Pretend you did but don't? Make up another exercise that doesn't cause pain?