Vantage theme is not working with multisite sigup page
I installed mulitsite in my site inphnompenh.mobi few days ago. With vantage theme, all the pages in my site are working ok except for
www.inphnompenh.mobi/wp-signup.php. I have followed the instruction in
http://codex.wordpress.org/Create_A_...s_Requirements. Since then, I have got a network dashboard along with my site dashboard in the backend. So far, i haven't seen any error, all the pages in my sites are running as usual with vantage themes, but only this page
www.inphnompenh.mobi/wp-signup.php that has no header, widget and etc of vantage theme. but when I switch to Twenty Thirteen theme, that signup page has the header, the widget and etc of Twenty Thirteen theme. can someone please advise me as to how to fix it, so that the signup page work with vantage theme. Thanks in advance.