A similar problem occurred in my case.
Following is the ssl server configuration.
At first I used AJP.
But after I could not find a corresponding directive to proxy_ssl_session_reuse, I changed to proxy.

upstream loadbalancer {
server 127.0.0.1:8080;

keepalive 100;
}

server {
listen 443 default ssl;
ssl on;

......

location / {
#access_log off;
#ajp_pass loadbalancer;
proxy_pass http://loadbalancer;
proxy_ssl_session_reuse off;
}
}


Here's the error log:
2012/02/08 15:03:49 [info] 13273#0: *1 SSL_do_handshake() failed (SSL: error:14094416:SSL routines:SSL3_READ_BYTES:sslv3 alert certificate unknown) while SSL handshaking,

Any help would be greatly appreciated!
Thanks in advance!