nginx 500 Internal Server Error

When I access 127.0.0.1:6789 it works fine, but when i try to access something like 127.0.0.1:6789/busca.html?q=a, I got 500 Internal Server Error

this is my nginx config file

server {

    listen   88;


    root /vagrant/rizqcursosonline/rizqcursosonline/frontend/wwwpublic;
    index index.php index.html index.htm;

    server_name example.com;

    location / {
            try_files $uri $uri/ /index.html;                
    }

    error_page 404 /404.html;

    error_page 500 502 503 504 /50x.html;
    location = /50x.html {
          root /vagrant/rizqcursosonline/rizqcursosonline/frontend/wwwpublic/;
    }

    # pass the PHP scripts to FastCGI server listening on 127.0.0.1:9000
    location ~ \.php$ {
            try_files $uri =404;
            fastcgi_pass unix:/var/run/php5-fpm.sock;
            fastcgi_index index.php;
            fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;
            include fastcgi_params;

    }

}

nginx log error

2014/04/12 18:16:32 [error] 4165#0: *5 rewrite or internal redirection cycle while internally redirecting to "/index.html", client: 10.0.2.2, server: example.com, request: "GET /busca.html?q=a HTTP/1.1", host: "127.0.0.1:6789", referrer: "http://127.0.0.1:6789/"

2014/04/12 18:16:32 [error] 4165#0: *7 rewrite or internal redirection cycle while internally redirecting to "/index.html", client: 10.0.2.2, server: example.com, request: "GET /favicon.ico HTTP/1.1", host: "127.0.0.1:6789"

instead of

try_files $uri $uri/ /index.html;

I used

try_files $uri/ $uri /index.php?$query_string;