private.php and search.php white page

[pompaunpo]

My forum ( vBulletin version 3.6.4.)
http://www.nscale.org/forum/index.php
work very well, but for two days only 2 link show a white page,
private.php (view Private Messages) and search.php (all SEARCH and NEW POSTS).
show a completely white page without errors
I, in the time, have active any add-ons, but I have not installed new add-ons or plug-in in the last days,
I have add only little mod for the Google Search in home page and not have modificate template!

I have disabled the Google Search mod, I have restored header, headinclude and phpinclude templates with the original templates, I have restored private.php and search.php files with the original files,
but nothing !!! private.php and search.php continue again to show a white page.

why? ....could it depend $session variable ?

who help me?

thanks