How to add a subdomain in user account

Hi,
  There is a huge problem in adding sub domain. If a user want to add subdomain like
/newsite/public_html
/username/newsite/public_html
/home/username/public_html/newsite
 anything like this the user can not able to add subdomain & its give error saying that "ERROR! User Mismatch, please contact your system admin."

But the same way /newsite/public_html  has given from admin account the subdomain has created successfully.

So please check and resolve this & also suggest what way the user can do to add subdomain.

Please add features for zip and unzip, file editior in html way for users.add some dns manages so user can do  not bu using Free DNS Manager(which added by your side) because some time it get fail .

Regards