ERROR Exception of type 'System.Web.HttpUnhandledException' was thrown.
Message:Response.Redirect cannot be called in a Page callback.
That looks like it's trying to do the built-in redirect to force the customer to sign in before hitting the account.aspx page. As for the '...in a Page callback' part - as you'd expect from the message, that error is generally seen when an app tries to do a Response.Redirect while processing what the .NET platform thinks is a callback (often triggered by a POST with a querystring).
That's not something we've seen before in the OOB software, though under certain conditions I suppose it might be possible if a logged-in customer sat on the account page long enough for the session to end, and then clicked a button to submit a change to account info. That doesn't seem like something that would happen often though. What kinds of modifications have been made to the site?