AJAX :: System.ArgumentOutOfRangeException 'ComboBox' Has A SelectedIndex Which Is Invalid ?

Synopsis: I have a AJAX enabled ASP.Net application, the purpose of which is to allow users to ad hoc drill an engineering database. The application UI is divided into three sections, Filtering, Column Selection, and Results. The filtering section (implemented as a user web control) uses a PlaceHolder control, to which I allow addition and removal of individual Filter user controls.

All of that works well. The Filter user control essentially consists of three ComboBox controls with SqlDataSources bound to each of those ComboBoxes, and a TextBox to enter in a value. The first ComboBox, once a value is selected in its list, passes the SelectedValue to the SqlDataSource of the next ComboBox, which uses that value as a Select Parameter so the DataSource can fill out the ListItems of the next ComboBox. So simply, the results of the previous one cascade to the next.

Again, all this worked well. But one of the requirements was to allow storage of these queries the customer comes up with, allowing them to reload the query at a later time to run again.

I implemented that by writing a simple set of container classes, Filter, Column, and Query, where Query has public arrays of Filters and Columns. I serialize that simple Query object, then store it as XML in my database. To reload it, I de-serialize the xml, and rebuild the Query object, which I then use in turn to rebuild the Filters and Columns.

And that is the problem. I am rebuilding the query, and I think I am setting up the Filters correctly. Everything reloads on the page, just as I had saved it. But then when I try to use the query, I get the error

System.ArgumentOutOfRangeException 'ComboBox' has a SelectedIndex which is invalid because it does not exist in the list of items. Parameter name: value

I believe the problem is that the SelectedIndex is attempting to set the index for the ComboBox before the DataBind occurs during a postback.What is curious about this is if I hadn't tried to load and initialize these controls myself and just added a bunch of fliters setting ComboBoxes as I go, it has no problem maintaining the SelectedIndex, the list of values in the ComboBoxes and so on during a postback. I don't believe in that case it is even doing a DataBind for those controls.