Invalid postback or callback argument.

Today I ran into this error when posting back on my ASP.NET page.

System.Web.HttpUnhandledException (0x80004005): Exception of type ‘System.Web.HttpUnhandledException’ was thrown. —> System.ArgumentException: 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.
at System.Web.UI.ClientScriptManager.ValidateEvent(String uniqueId, String argument)

It did not take me long to track down the problem. I forgot to add an ID to a dynamically created dropdownlist control.

 

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