Anonymous Users Can't Access Sub-Domain sites

I have four domains, which are attached with four separate themes. Like:

example.com - ninesixth theme
awc.example.com - ninesixth_awc theme
student.example.com - ninesixth_student theme
courier.example.com - ninesixth_courier theme

The primary domain is working okay. But when anonymous user visit awc.example.com, its shows part of content from Primary domain theme but not showing content from subdomain theme. But if i logged in as "Admin", it shows the sub-domain with the theme attached with it. Did not find any permission related to it.

What I found that $conf['theme_default'] is not set the sub-domain theme name.

Please help.