There was a bug in install script. And during pro active chat invitation creation you could get white screen. So just execute this query:

ALTER TABLE `lh_abstract_proactive_chat_invitation`
ADD `show_random_operator` int(11) NOT NULL,
COMMENT='';

This bug in install script effected 1.63v and 1.64v.

Really sorry for this. But, bad things happens to good people :)