I'm playing solo as a bard with the barbarian as a sidekick, and have reached the pinnacle of the Wizard's tower in Luskan. Arabeth, Maugrin, and the other one are behind a grille gate, along with a bunch of orc warriors. I can kill the warriors with arrows or by summoning my bear, but I can't get the gate open, and nothing touches the three characters.

What am I missing?

Thoon the Baffled

Well... some sort of cutscene should appear, and you shouldn't kill anyone just yet. Just walk around a bit, and check if it starts anyway. Otherwise this may be a bug. Have you installed the latest patch?

I had the same. Quite buggy, although there have been some patches since. I'm not entirely sure how I triggered the rest of the game, but if it was not using a stone of recall then it was something else on the roof or in the little room attached to it.

If you look carefully you will notice that the three characters are having a conversation. Stay near the gate and watch the conversation. At some point they will notice you and the gates will open. The only way to leave the roof is with the stone of recall.

sigh ... I stood in front of the gate for an hour ... nothing. I uninstalled the game. reinstalled it, installed the latest patch (1.29) and played from a saved game on the 4th level back to the top. Guess what! Same thing. Gate won't open.
I had already used the stone of recall to go back to the temple, re-enter the front door of the tower, and go back to the pinnacle. No help.

thoon