Good day folks,
I am writing an Excel import class in Ax 2012 R2 and I'm having an issue with SysExcelWorkbooks trying to access itemFromNum() with the below error.

Is there anything with the code I have written, which is below?
SysExcelApplication _application;
SysExcelWorkbooks _workbooks;
SysExcelWorkbook _workbook;
SysExcelWorksheets _worksheets;
SysExcelWorksheet _worksheet;
SysExcelCells _cells;
//table names and EDT declaration omitted here
COMVariantType _type;
int rowCount=1;
container _conFilter = ["(.xls)" ,"*.xlsx"];
FileName _fileName;
Dialog _dialog;
DialogField _dialogfield;
_dialog = new Dialog();
_dialog.caption("Pick a file");
_dialogfield = _dialog.addField(extendedTypeStr(FilenameOpen));
_dialog.filenameLookupFilter(conFilter);
_dialog.run();
if(_dialog.closedOk())
{
_fileName = _dialogfield.value();
_application = SysExcelApplication::construct();
_workbooks = _application.workbooks();
try
{
_workbooks.open(_fileName);
}
catch (Exception::Error)
{
throw error("Could not open the excel upload file");
}
_workbook = _workbooks.item(1);
_worksheets = _workbook.worksheets();
_worksheet = _worksheets.itemFromNum(1);
//more code here
}
Thank you in advance for your help!