Web Forms :: Error On Invalid Value In Dropdown With Autopostback True

I am getting the following error as 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. when an invalid value is passed in dropdown with autopostback=true. What should I do. I want the solution with "EventValidation=true" and "ValidateRequest=true" in the Page directives. Also without any Custom Error Pages Enabled in web.config file i.e Custom Error Pages are off in web.config file.