Datagridview sorting... Object must be of type Int32 exception

I coded a datagridview so that whenever the last row is clicked a new row automatically gets created. I also insert an incremental number in the first column of the new row and I simply want the entire grid to always remain sorted by that column. When the user edits the column, I first validate it to be an integer and then I call the following sort operation on the datagridview's _CellValueChanged event.