I decided to enumerate all the map errors I could think of.

Name errors: any error in which someone's name is persistently not what you'd expect.

• Quirrell being named Defense Professor.
• Anyone (probably Quirrell, maybe Harry) being named Tom Riddle.
• Quirrell or Harry being named Heir of Slytherin.

Map errors: any error in which the map itself is drawn incorrectly, or in a way you wouldn't expect.

• The Chamber of Secrets entrance being drawn on the map if/when Quirrell accesses it.
• Quirrell being drawn inside a wall if/when Quirrell accesses the Chamber of Secrets.
• If Quirrell can become a spirit, Quirrell being drawn inside a wall when he is in fact inside a wall.
• Harry being drawn in strange and incorrect places when he's inside of his trunk.

Name persistence errors: any error in which someone changes names.

• Harry changing names while using his "dark side."
• Quirrell switching between Quirinus Quirrell and "Defense Professor," possibly when Quirrell "rests."
• Quirrell being labeled Salazar Slytherin, particularly when he accesses wards.
• Harry being labeled something more commonly associated with Professor Quirrell when he uses his Potterdar.

Multiple dot errors: any error in which one person is in multiple places.

• If the Dark Lord can become disembodied (perhaps while Quirrell is "resting"), separate "Quirinus Quirrell" and "Defense Professor" dots in different locations.
• Any student with a Time-Turner showing up twice on the map.