Cannot Complete Quest "It Tolls For Us" (PS3)

I've fulfilled all the prerequisites for the quest "It Tolls For Us" and gone back to the NPC to complete the quest, however I cannot speak to him now.

The NPC is Liautroix who stands atop the tower at the Whitebrim Front (Coerthas Central Highlands)

The check mark is clearly above the NPC's head and the Journal states I should return to him.

Whenever I select the NPC in question and press "X" to initiate the completion of the quest all that seems to happen is that the icons on my hotbar grey out momentarily.

Any help with this would be appreciated!

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