The "lowest" applicable index for referring to a cell in an Excel sheet is [1,1], which corresponds to Column A, Cell 1. I see you're trying to refer to 0,0 which is out of the bounds of the table.
Though C# typically utilizes zero based table indexing, it appears the programmers of Excel Interop adhered to a different methodology. That or they wanted to keep their conventions uniform, since the first row in an Excel table starts with 1, and not 0. I'm not an Excel buff, but that's my best guess.
Edit: Per Siddharth's request, here's an example that copies the contents of a DataGridView control to an Excel sheet. Note that this just demonstrates basic functionality, and isn't a complete example or necessarily best practice:
#using Microsoft.Office.Interop;
Excel.Application xlApp;
Excel.Workbook xlWorkBook;
Excel.Worksheet xlWorkSheet;
xlApp = new Excel.ApplicationClass();
xlWorkBook = xlApp.Workbooks.Add(1);
xlWorkSheet = Excel.Worksheet xlWorkBook.ActiveSheet;
// Notice the index starting at [1,1] (row,column)
for (int i=1; i<DataGridView.Columns.Count+1; i++)
xlWorkSheet.Cells[1, i] = DataGridView.Columns[i - 1].HeaderText;
for each(DataGridViewRow row in DataGridView.Rows)
{
for each (DataGridViewColumn column in DataGridView.Columns)
{
xlWorkSheet.Cells[row.Index+2,column.Index+1] = DataGridView.Rows[row.Index].Cells[column.Index].Value;
}
}
Notice the disparities between the indexing. This example first copies the headers from the DataGridView, then offsets the position in the Excel sheet to copy the rest of the data since the column headers don't count as index-able cells in the DataGrid. This would probably also work for DataTables.
