The 'certificate code error' issue is a caused by the router using a self signed certificate and I assume you're using Chrome browser to access the router over HTTPS. The browser is sending an alert back to the router that the certificate in use is not from a known and trusted CA.
If you were to install a certificate on the router from a known trusted CA then this would not happen.
The error message is safe to ignore, or can be filtered out of the event log with the CLI command (use telnet, ssh or 'Execute a command' in the GUI):
event 0 ev_filter 98
Ben - Digi Support