[Forum] interbnal server error 500

[infora]

Hi,
I migrate from 4.x to 4.18 a short time before I changed of server (centOS5.3/php5,2.10,mysql5.0.51a). Every test works fine with admincp. Zend engine 2 is used.
Backup and restore : no problem. We detect some minor error but it seems to us vbulletin works properly
However we get one ton of error 500 (internal error).
I looked at some script in the server and see nothing special
And then I reacall of redirect URL problem.The structure of website is :
Index.html
….Some files
(directory :upload) and inside forum.php.
note : admincp has an other name XXXXX
When Xenus look at the whole website, he looks at vbulletin like external file of the website. Why ?
When we force it to look at the upload directory, we get one million error messages like that :
http://…………../upload/calendar.php?c=1&week=1148169600
errorcode: 12002 (timeout), linkedfrom page(s):
http://…../upload/calendar.php?c=1&week=1148774400

http://………/upload/calendar.php?do=getinfo&day=2006-4-30&c=1
errorcode: 12002 (timeout), linkedfrom page(s):
http://……../upload/calendar.php?c=1&week=1148774400

http://www............upload/css.php?styleid=1&langid=4&d=1321820469&td=ltr&sheet=additional.css
errorcode: 204 (no info to return), linkedfrom page(s):
http://…………………./upload/forum.php

http://--------/upload/images/2f misc/2f blog/2f top-highlight/2e png
errorcode: 404 (not found), linkedfrom page(s):
http://--------/upload/css.php?userid=190&cssuid=0&d=1322143851&td=ltr&styleid=0&sheet=userprofile.css

When w3clinkchecker runs, we get one ton of error 500
Nothing special in the log of the server.
So that vbulletin coud be the culprit.
So that raise the questions :
1) How should be the written the URL in admin cp (see the structure of website above)
2) Do we have (and in which folder we have) to place the file vb_dir.php
3) The most important : what should be the content of htacess ? (actually there’s none)