When creating a formula, it is possible a mistake may occur. The formula is not evaluated and Excel displays an error value or message. The common error values that could appear when creating a formula are described below: 

#VALUE        This error value is displayed if you use a cell reference in a mathematical formula that contains a piece of text. This error also appears if a selection is used without specifying a function.

#DIV/0!               This error value is displayed if you divide a value by zero (O).

#REF!           This error value is displayed if cell reference does not exist that
is used in the formula.

#N/A!           This error value is displayed if value is not available or Excel
cannot find the required value.

  Circular            The circular reference is a special error message displayed in

   Reference       form of dialog box. This error message occurs when a formula uses its own result as one of its reference or arguments. This error message is also indicated in the status bar showing the cell address containing the error.