Manage Permission to SharePoint Group

i want to make user enable to manage all the permission related work. i.e. he can delete/Add users from any group in the site.

what i did, i put the user in "Owner Group" then go the permission page 

http://intranet/xyz/xyzy/_layouts/user.aspx

then i click on the particular Group and i got "Access Denied" error .

please guide me if i am doing any thing wrong ?