Invalid postback or callback argument. Event validation is enabled using ''

Question

I am getting the following error when I post back a page from the client-side. I have JavaScript code that modifies an asp:ListBox on the client side.

How do we fix

Answer 1

We ran into this same issue when we were converting our regular ASPX pages to Content pages.

The page with this issue had a tag within one of the Content sections, thus two form end tags were rendered at run time which caused this issue. Removing the extra form end tag from the page resolved this issue.