Nostalrius Begins - Quality wow vanilla realm (1.12)

Was waiting to do the deadmines with a friend and three strangers. While waiting for them to finish their previous run I was asked by a level 54 hunter to join his party, so that he could reset his dungeon. I followed him around for a while, and after a couple of minutes I left the instance and then left his party, so that I could join up with my friend.

Here's the problem though, after joining my friend's party I couldn't enter the dungeon again. Running into the instance was like running into a wall, and I couldnt get it. We tried re-creating the party, relogging, exiting the entire client, you name it. It still wouldnt let me in. Hoping someone can explain why this happened, and help me fix it.