I get the same problem with TECK
The difference is my homepage is work well, but when I tried to click a link on my homepage, it's get me 500 Internal Server Error.

Here my configuration:

if (-f $document_root/maintenance.html) {
rewrite ^(.*)$ /maintenance.html last;
break;
}

location / {
error_page 404 = //index.php?q=$uri;
try_files $uri $uri/ /index.php?q=$request_uri;
}

location /administrator/ {
rewrite ^(.*)$ https://www.domain.com$1 permanent;
}

if ($request_uri ~* "com_login") {
rewrite ^(.*)$ https://www.domain.com$1 permanent;
}

location /en/ {
index index.php;
error_page 404 = //index.php?q=$uri;
if (!-e $request_filename) {
rewrite ^/en/(.*)$ /en/index.php?$1 last;
break;
}
}

location /en/administrator/ {
rewrite ^(.*)$ https://www.domain.com$1 permanent;
}

location ~ \.php {
fastcgi_pass 127.0.0.1:9000;
fastcgi_index index.php;
fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;
include /usr/local/nginx/conf/fastcgi_params;

and some output from error_log :

2011/06/15 19:41:54 [error] 1985#0: *208 rewrite or internal redirection cycle while internal redirect to "//index.php", client: 66.249.72.65, server: www.domain.com, request: "GET /agenda.html HTTP/1.0", upstream: "fastcgi://127.0.0.1:9000", host: "www.domain.com"
2011/06/15 19:41:55 [error] 1985#0: *213 rewrite or internal redirection cycle while internal redirect to "//index.php", client: 203.130.206.49, server: www.domain.com, request: "GET /diploma.html HTTP/1.0", upstream: "fastcgi://127.0.0.1:9000", host: "www.domain.com", referrer: "http://www.domain.com/"