Last three days I've had the same issue with a lvl 20 character. When I q for random normal and I get any CP player in the group, I get an error message saying my CP is too low when the party is formed. Even though we are all queuing for normal dungeon. Travelling to player already in dungeon doesn't work at all - nothing happens, not even an error message.
First day, everyone else was CP and I was the only under 50. Eventually they kicked me from group so I could avoid the penalty but I still got the 15 min penalty. Last two days, it has been mixed party and all the non cp players had the same issue and could not port in to the dungeon. Whether you get kicked or leave the group, you end up with the 15 min penalty.
I was solo queuing as tank in each of the cases.