Sometimes Excel can't calculate a formula because the formula contains an error. If that happens, you'll see an error value instead of a result in a cell. Here are three common error values:
# # # # # The column is not wide enough to display the contents of this cell. Increase column width, shrink the contents to fit the column, or apply a different number format.
#REF! A cell reference is not valid. Cells may have been deleted or pasted over.
#NAME? You may have misspelled a function name or used a name that Excel does not recognize. You should know that cells with error values such as #NAME? may display a color triangle. If you click the cell, an error button 
appears to give you some error correction options.
In this case, the user typed Summary, which is not an Excel function.