Domain Mapping Error 403/500

Hi everyone. What am I missing with my configuration, because I keep getting a 403 Error when I try to visit a site for which I’ve mapped a domain? I am super over my head here.

I’m using the subdirectory setup to create the many sites.

Info – Host: Lunarpages. Created subdomains, ie, alpha.flingem.com.
Added CNAME for alpha.flingem.com pointing to flingem.com (wordpress is installed in root directory). There is also an A record for flingem.com pointing to the IP address of the server. It is a dynamic IP.

In WPMS – In Network Admin>Settings>DomainMapping> i put the value flingem.com in the CNAME field. In Network Admin>settings>Domains i mapped alpha.flingem.com to site id 7 and marked it as primary.

When I try to access the site through the url alpha.flingem.com, i get this error 500:
“Internal Server Error -The server encountered an internal error or misconfiguration and was unable to complete your request.”

I am using lunapages hosting, and i noticed that when I created a subdomain(alpha.flingem.com), that it automatically created subdirectories on the server with the folder name that matches the one I created in WordPress. For example, in the WP site is flingem.com/alpha, and when i created the subdomain alpha.flingem.com in lunarpages, an alpha subdirectory appeared on the server. It was empty, except for an empty directory inside it of cgi-bin. Is this a conflict? I’m ashamed to say I deleted it, because i was receiving a 403 error, but was able to access my site through the flingem.com/alpha url after that.

I am really confused as to what I’m doing wrong. Does anyone notice anything i need to fix?

Thanks.

Jennifer