Fixing error registration page with theme and buddypress/multisite

Hi,

Anyone has been already experiencing this type of errors on the registration buddypress page:
Fatal error: Call to undefined function bp_blogs_subdomain_base() in /wp-content/themes/u-design-BuddyPress-child/registration/register.php on line 195

It can be theme related but I don't have any idea on how to fix it?Changing of theme because of that will be a sad choice

Thanks in advance