just remove OnItemDataBound="subContractors_ItemDataBound"
from your aspx page
Edit this error occurred because you don't have subContractors_ItemDataBound
method in .cs file to handle OnItemDataBound
event , so you have to handle OnItemDataBound
event or just remove OnItemDataBound="subContractors_ItemDataBound"
Edit to bind list of strings use :
<asp:Label ID="SubCon" Text='<%# Container.DataItem %>' runat="server"></asp:Label>