I have read your article "AJAX Cascading DropDownList using jQuery in ASP.Net", I have everything working correctly, great article, easy to follow and implement.
FYI: I found a jquery plugin to simplify working with select boxes: http://www.texotela.co.uk/code/jquery/select/
Question: How are you handling the exception:
Invalid postback or callback argument. Event validation is enabled using <pages enableEventValidation="true"/> in configuration or <%@ Page EnableEventValidation="true" %> in a page. For security purposes, this feature verifies that arguments to postback or callback events originate from the server control that originally rendered them. If the data is valid and expected, use the ClientScriptManager.RegisterForEventValidation method in order to register the postback or callback data for validation.
I do not want to set EnableEventValidation for the whole page, how would you recomend to address this?