DataTables : "Cannot read property 'className' of undefined" after adding aoCoumns

DataTables : "Cannot read property 'className' of undefined" after adding
aoCoumns

the datatable was working without any problem ! Problem started when i
started using this
'aoColumns': [
null,
null,
null,
{ 'sType': 'datetime-us' },
null
],
I used this property for sorting date Datatables:sorting date When i
uncomment this property it works (without date been sorted)