dear friends, we had discovered an incompatibility between RS Firewall and any 3rd party extension that is rendering an user email.
When user data are detected, opc prints them within OPC themes at the checkout page, but RS Firewall is trying to convert the email addresses into images which breaks the checkout in VM or OPC generally.
The problem when an email address if found may look like this:
Current solution until RS Firewall adjusts it's code is to disable the email protection feature in RS Firewal:
best regards, stan, rupostel.com