I have a dropdownlist which has been populated
ddlNumbers.DisplayMember = \"PhoneNumber\";
ddlNumbers.DataSource = mobileList;
ddlNumbers.SelectedItem = null
You can't remove an item from a list when its bound to a control, You can temporarily null
the data source of the bound control and remove the item from list and then set the data source again.
Something like,
//Null the datasource
Combobox1.Datasource = null;
//Remove the item
ddlMobileNumbers.Items.RemoveAt(i);
//Set the source again
Combobox1.Datasource = ddlMobileNumbers;