The AnimationClip 'Attack' used by the Animation component 'Knife' must be marked as Legacy.

So yeah, help would be appreciated. This is my script:

#pragma strict

var TheDammage : int = 50;
var Distance : float;
var MaxDistance : float = 1.5;

function Update ()
{
	if (Input.GetButtonDown("Fire1"))
	{
		animation.Play("Attack");
		var hit : RaycastHit;
		if (Physics.Raycast (transform.position, transform.TransformDirection(Vector3.forward), hit))
		{
			Distance = hit.distance;
			if (Distance < MaxDistance)
			{
				hit.transform.SendMessage("ApplyDammage", TheDammage, SendMessageOptions.DontRequireReceiver);
			}
		}
	}
}

When importing animations, check the import inspector (comes up when you select the animation object or FBX or whatever in the Assets folder).

Under “Rig”, you can select “Legacy”.