httpserver: client can spam logs with certificate errors

i am using https with tornado like this:
server = httpserver.HTTPServer(application , ssl_options={ "certfile": os.path.join(app_dir, "cert.pem"), "keyfile": os.path.join(app_dir, "key.pem"), } )

however, tornado throw the warning below:
WARNING:tornado.general:SSL Error on 22 ('192.168.1.100', 56992): [SSL: SSLV3_ALERT_CERTIFICATE_UNKNOWN] sslv3 alert certificate unknown (_ssl.c:590) WARNING:tornado.general:SSL Error on 23 ('192.168.1.100', 56994): [SSL: SSLV3_ALERT_CERTIFICATE_UNKNOWN] sslv3 alert certificate unknown (_ssl.c:590) WARNING:tornado.general:SSL Error on 19 ('192.168.1.100', 56989): [SSL: SSLV3_ALERT_CERTIFICATE_UNKNOWN] sslv3 alert certificate unknown (_ssl.c:590) WARNING:tornado.general:SSL Error on 21 ('192.168.1.100', 57007): [SSL: SSLV3_ALERT_CERTIFICATE_UNKNOWN] sslv3 alert certificate unknown (_ssl.c:590) WARNING:tornado.general:SSL Error on 22 ('192.168.1.100', 57008): [SSL: SSLV3_ALERT_CERTIFICATE_UNKNOWN] sslv3 alert certificate unknown (_ssl.c:590) WARNING:tornado.general:SSL Error on 24 ('192.168.1.100', 57010): [SSL: SSLV3_ALERT_CERTIFICATE_UNKNOWN] sslv3 alert certificate unknown (_ssl.c:590) WARNING:tornado.general:SSL Error on 23 ('192.168.1.100', 57009): [SSL: SSLV3_ALERT_CERTIFICATE_UNKNOWN] sslv3 alert certificate unknown (_ssl.c:590) WARNING:tornado.general:SSL Error on 21 ('192.168.1.100', 57019): [SSL: SSLV3_ALERT_CERTIFICATE_UNKNOWN] sslv3 alert certificate unknown (_ssl.c:590) WARNING:tornado.general:SSL Error on 19 ('192.168.1.100', 57017): [SSL: SSLV3_ALERT_CERTIFICATE_UNKNOWN] sslv3 alert certificate unknown (_ssl.c:590) WARNING:tornado.general:SSL Error on 22 ('192.168.1.100', 57022): [SSL: SSLV3_ALERT_CERTIFICATE_UNKNOWN] sslv3 alert certificate unknown (_ssl.c:590) WARNING:tornado.general:SSL Error on 25 ('192.168.1.100', 57039): [SSL: SSLV3_ALERT_CERTIFICATE_UNKNOWN] sslv3 alert certificate unknown (_ssl.c:590) WARNING:tornado.general:SSL Error on 21 ('192.168.1.100', 57032): [SSL: SSLV3_ALERT_CERTIFICATE_UNKNOWN] sslv3 alert certificate unknown (_ssl.c:590) WARNING:tornado.general:SSL Error on 21 ('192.168.1.100', 57048): [SSL: SSLV3_ALERT_CERTIFICATE_UNKNOWN] sslv3 alert certificate unknown (_ssl.c:590)
what does the warning mean? and how can i fix it?

Start at the HTTPServer SSL handling entry point described in the report and trace where certificate errors are logged. Determine the intended behavior for repeated client certificate failures; done should include a documented resolution and coverage for the reported log-spam case.