Re: Problems with sprintf in translation
bp-groups.php line 1005, right?
'content' => apply_filters( 'bp_groups_created_group_activity', sprintf( __('%s created the group %s', 'buddypress'), $user_link, '<a href="' . $group_link . '">' . $group->name . '</a>') . ' <span class="time-since">%s</span>', $user_link, $group_link, $group->name )
As Arturo’s suggested, check you are working from the .pot file that comes with 1.0. It’s possible it was changed since an older version thus your translation not being applied.