Data update issue by dropdownlist after populate from gridview.

Hello , I had populated data from gridviview to external dropdownlist thru Gridview_SelectedIndexChanged {  DropDownList1.SelectedItem.Text = GridView2.SelectedRow.Cells[3].Text.ToString(); } Now want it to insert into SQL table as value . But unfortunately appeard error " Question Mark" . Please help me how i insert value without any error