Secure subdomain configuration

Hello everybody,
I had amember4 configured this way:
aMember Folder: /members
Root Url: http://www.mydomain.com/members
Secure Root Url: https://mydomain.com/members
Now my cert endend and I want to renew it but I'd like to use https://secure.mydomain.com/members instead of https://mydomain.com/members so I created the subdomain, pointing directly to /members, install the cert and changed the configuration in amember but everytime I go there I get 500 Internal Server Error with apache log "Request exceeded the limit of 10 internal redirects due to probable configuration error"
Is there a place that explains how to deal with this configuration? Is is possible to configure amember this way?
Thank you very much.

Alexander, thak you for your answer, this is the file's content, I think I didn't touch it, just fixed the folder:

# Sample Nginx rules configuration:
# aMember rules (replace /amember to actual aMember Pro path from site root)
#
# location ~* ^/amember/.*\.(js|ico|gif|jpg|png|css|swf|csv)$ {}
# location ~* ^/amember/setup/index.php$ { try_files not-existing-file @php; }
# location ~* ^/amember/js.php { try_files not-exiting-file @php; }
# location ~* ^/amember/index.php$ { try_files not-existing-file @php; }
# location ~* ^/amember/public.php$ { try_files not-existing-file @php; }
#
# location ~* ^/amember/public { rewrite ^.*$ /amember/public.php; }
# location ~* ^/amember/setup { rewrite ^.*$ /amember/setup/index.php; }
# location ~* ^/amember { rewrite ^.*$ /amember/index.php; }
#
# you must already have something like that in your nginx configuration:
#
# location ~ \.php$ {
# try_files not-existing-file @php;
# }
# location @php {
# fastcgi_pass 127.0.0.1:9000;
# include fastcgi_params;
# }
#
# it is necessary to have @php section, as it is referred by aMember rules, and
# it must be located at bottom
#
#
<IfModule mod_rewrite.c>
RewriteEngine on
RewriteBase /members
RewriteRule ^public public.php [L]
RewriteRule ^js.php js.php [L]
RewriteRule !\.(js|ico|gif|jpg|png|css|swf|csv)$ index.php
</IfModule>

<IfModule mod_php5.c>
php_flag magic_quotes_gpc off
</IfModule>