[Plugin: Visual Form Builder] Nonce error on Submit

Have had several successful form submissions, but the last three or four have failed with the following error: Security check: unable to verify nonce value.
When I try it while logged in as an admin it goes through, but if I log out and go through it fails with this error.

Here’s the link to the page w/the form http://www.anshaiemeth.org/2012/08/20/online-religious-school-registration/

http://wordpress.org/extend/plugins/visual-form-builder/