The othello Error (Ekman, 1985) refers to the Sheakspeare's play of Othello killing his wife who he suspected to love another man. All this based upon his wife's distress failing to listen to her alternative innocent explanations. 

The interpretation of behaviour. 
When a subject under questioning show signs of fear and/or distress it could indicate the subject is not telling the truth. The Othello Error refers to the fact that honest people may experience fear during questioning and show signs of fear while perfectly telling the truth. 
In essence you can not rely entirely on signs of fear as an indicator of truth or lie. You have to look beyond the signs.