private.php and search.php white page

[pompaunpo]

I check all template, the problem is in $session variable

SESSIONURL is correctly in my headinclude:

<script type="text/javascript">
<!--
var SESSIONURL = "$session[sessionurl_js]";
var IMGDIR_MISC = "$stylevar[imgdir_misc]";
var vb_disable_ajax = parseInt("$vboptions[disable_ajax]", 10);
// -->
</script>

but in HTML source the variable SESSIONURL is empty

IMGDIR_MISC and vb_disable_ajax is correct but SESSIONURL si empty

what is the file that send this variable as could I check
if it is corrupt ?