If you are trying to generate a new token from a link in an email you received, then that email is a Phishing attempt to get your info. NEVER click on any links in an email you receive. If you are getting the error but going to Auctiva by typing in your browser, then you need to file a support ticket so they can help you.
That said, there was an issue a couple of days ago between Firefox & eBay where "Beware, Forgery" messages were popping up. That has since been corrected by eBay.
If you are still having trouble, contact Support and they will help you.