Invalid postback or callback argument. Event validation is enabled using
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 valida
I have found the same problem posted by people and it turns out that the problem comes from the webconfig file:
<pages validateRequest="false" enableViewStateMac="true" enableEventValidation="true" viewStateEncryptionMode="Always">
The enable validation is set to "true" - but I don`t want to turn this to false because it will cause security issues on the site. What would be the workaround this please? Anyone had the same error when using dynamic dropdowns?