logout error , got blank page

I’ve installed WPMU2.8.5.2 and buddypress1.1.2, and it works but have one issue with logout from site, for example : if admin wanna to logout from the main page of buddypress , will get the blank page on screen and a url in the browser addrees field as below.if not at main page to logout, do not get the blank page, it works well.

http://xxxxxxx.com/wp-login.php?action=logout&redirect_to=&_wpnonce=0bf06bd852