When you launch a form with a GridView that has a DropDownListBox as one of the column fields, and the drop-down list field doesn’t contain an empty string value item, you might get the following .NET exception error at runtime:
[ArgumentOutOfRangeException: '[DROPDOWNLISTBOX_ID]' has a SelectedValue which is invalid because it does not exist in the list of items. Parameter name: value] System.Web.UI.WebControls.ListControl.PerformDataBinding(IEnumerable dataSource) +1379 System.Web.UI.WebControls.ListControl.OnDataBinding(EventArgs e) +408 System.Web.UI.WebControls.ListControl.PerformSelect() +44 System.Web.UI.Control.DataBindChildren() +248 ...
This is a known behavior due to the data binding nature of the GridView and the DropDownListBox controls.
System.ArgumentOutOfRangeException is raised when the GridView tries to bind the default value (which is an empty string) to the missing empty string value item in the drop-down list field in the GridView in Edit mode.
The solution is to always keep an empty string value item (with a
Select an item text, for example) in the DropDownListBox field.