[solved]error 404 on http://portalurl.com/user

[admin]

RewriteRule ^([^/\.]+)?/?$ user.php?username=$1 [L,QSA]

This line is required. There is two solution for sub domain.

1. Create sub domain as independent domain with its own cpanel account. Only possible if you have WHM access.

2. add following line for each of the sub domain in the .htaccess

RewriteRule ^subdomain$ - [L]
RewriteRule ^subdomain/(.*) - [L]