Cause
You can get this Uptime Monitoring error in your Location Fail Log if your web server does not support SSL Secure Renegotiation.
This is a severe SSL vulnerability (CVE-2009-3555) that could allow an attacker to insert data into secured HTTPS sessions.
Fix
It is advisable to upgrade your server and use the current SSL protocols.
Alternative
If upgrading your server to use the current SSL protocols isn’t an option for you, then you can stop receiving this error by changing the Uptime Monitoring target to plain HTTP instead of HTTPS (i.e., if your monitored target is https://your-website.com you can change it to http://your-website.com to get rid of this SSL protocol check).