Repeated Nonce Errors from Multiple Users

Multiple users across multiple browsers are receiving nonce errors when attempting to register. Sometimes changing browsers works, but not always. Registration was working fine at site launch but this issue has become much more frequent the past two weeks and I am unclear what would have caused it. I have seen only one other thread with a similar concern. Is this a known issue and is there a fix for it?

The page I need help with: [log in to see the link]