When using a text field with a where statement I get "Invalid Column name" WHY?

SQL = "SELECT * FROM Employees where LastName = KING"
rs.Open SQL, dcnNWind, adOpenForwardOnly, adLockReadOnly

Using a number field everything is fine!

SQL = "SELECT * FROM Employees where Employee_ID = 7"
rs.Open SQL, dcnNWind, adOpenForwardOnly, adLockReadOnly


Thanx