The anti-forgery token could not be decrypted

Question

I have a form:

@using (Html.BeginForm(new { ReturnUrl = ViewBag.ReturnUrl })) {
@Html.AntiForgeryToken()
@Html.ValidationSummary()...

and a

Answer 1

I just received this error as well and, in my case, it was caused by the anti-forgery token being applied twice in the same form. The second instance was coming from a partial view so wasn't immediately obvious.