Today I've spent more than one hour trying to solve the following issue: I have a DropDownList control and I bind a collection of objects and then I set the SelectedValue to the first value from the collection. Here is the piece of code I've used:

 

ddlControl.DataSource = myCollection;

ddlControl.DataTextField = "Text";
ddlControl.DataValueField = "Value";

ddlControl.DataBind();

ddlControl.SelectedValue = "1";

 

  Everything was fine, but when I tried to rebind the same control to another collection of the same objects (a subcollection), I got the following error:

 

  This is a BUG and I solved this issue by replacing the code with a foreach statement and I added manually each item to the collection of Items.

ddlControl.Items.Clear();
foreach (Item item in items)
{
    ddlControl.Items.Add(new ListItem(item.Text, item.Value));
}
ddlControl.SelectedValue = "0";