The Tunnel Does Not Work

Hello again,

quest: Dwarves and Doguns Part I
I repaired the machine and got the dragon bone shark.
I knocked on the black block - it opened
but I cannot enter the black tunnel. I walk in and nothing happens.
sometimes Korzim appears an talks about earth and fire. The next second he ist gone.
I alway run against the black "wall" in the tunnel.....
I left the game and came back, but it's always the same

meanwhile I typed /kill an started the quest again - same problem