When hitting a button, an error would occur:

System.Web.HttpUnhandledException: Exception of type 'System.Web.HttpUnhandledException' was thrown. ---> System.ArgumentException: Invalid postback or callback argument. Event validation is enabled using in configuration or 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 then added EnableEventValidation="false" into my @Page directive, which fixed the error. Now after manipulating the listbox, the new values in the listbox are not posted back to the server. How can I solve this?