Requested unknown parameter

Can you help me understand why this error comes up?
DataTables warning: table id=list - Requested unknown parameter 'date' for row 0, column 1.

   "columns": [

        {
        "className":      'details-control',
        "orderable":      false,
        "data":           null,
        "defaultContent": '+'
        },  

        {"data": "date"},                              
        {"data": "name"},
        {"data": "lastname"},               
        {"data": "email"},                                              

    ],

The html is also correct. The json response does not give any error. I don't understand this.