I was having the same issue with WordPress 3.5.1 and plugin version 1.5.8. I was able to solve the issue by setting up custom pages for access denied on Authenticated and Anonymous users.
This is accessible from Settings -> Page Security. On the page that is loaded click the top check-box to the right of the label Use Custom Pages. The description of the check-box (to the right) is “Use pages for default access denied screens”. Protection Type radio button left at the default value of Redirect.