having a real issue pointing subdomain to specific folder

following these:

I have sub up.mydomain-name.com that needs to point to /domains/mydomain-name.com/public_html/forums/uploads

when I add this in the custom httpd config apache stops. I have not found any error (YET) showing why.

this is where cpanel really shines, wish DA could address this.
any ideas on how I can see why this is failing?