Perhaps someone can explain why you were denied access.

Once a year I fly from YYZ to YYJ via YVR on an Aeroplan J Award. As we all know, there is no J cabin on the DASH-8s. But I have always been allowed to use the MLL at YVR between my J flight from YYZ and the Y flight to YYJ. I am doing so in a few weeks and, as I have a two-hour connection, I'm hoping that policy is the same.