'ddlXXX' has a SelectedIndex which is invalid because it does not exist in the list of items

'ddlxXX' has a Selectedindex which is invalid because it does not exist in the list of items.
Parameter name: value

Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more @R_436_4045@ion about the error and where it originated in the code.
Exception Details: System.ArgumentOutOfRangeException: 'ddlxXX' has a Selectedindex which is invalid because it does not exist in the list of items.
Parameter name: value
Source Error:

Line 269:        ddlxxx.DataTextField = "Name"
Line 270:        ddlxxx.DataValueField = "id"
Line 271:        ddlxxx.DataBind() 
Line 272:        ddlxxx.Items.Insert(0, New ListItem("All", "-1"))
Line 273:        ddlStudents.Selectedindex = 0

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listOrgs.Items.Clear();
listOrgs.Selectedindex = -1;
listOrgs.SelectedValue = null;
listOrgs.ClearSelection();     // Clears the selection to avoid the exception (only one of these should be enough but in my application I needed all..)
listOrgs.DataSource = new Organization().DTListAll(SiteID);
listOrgs.DataTextField = "OrganizationName"; 
listOrgs.DataValueField = "OrganizationID"; 
listOrgs.DataBind();