Continuity mistake: Guy of Gisbourne says to Robin Hood that he should lay down his weapons. Robin Hood throws his bow and sword on to the ground. He then gets thrown down the cliff, into the river. A few minutes later, when we get focused on him again, we see that the bow is lying in the river with him. (00:06:05 - 00:10:55)
Audio problem: Near the end Robin's men all push barrels of oil over to to create a wall of fire, trapping the Sheriff and his guards inside the castle. When Robin picks up the flaming arrow he shoots it at the oil where it sticks firmly in the ground, but if you listen closely when the arrow hits the floor there is the sound of the arrow bouncing against stone - it couldn't make that noise if it hit the ground directly and stuck there.