Htaccess - File protection - Unable to downlload or Permission denied

Hi everybody,

New in the Drupal world, i have to manage an existing website.
The website's datas can only be downloaded by our registred users,

Q: Why doesn't i used the default file protection ?
There is unplubished nodes (for archiving) needed to be show in the local intranet.

Actual situation:
An .htacess have been placed in : \sites\default\files\.htaccess

SetHandler Drupal_Security_Do_Not_Remove_See_SA_2006_006
Options None
Options +FollowSymLinks

SetEnvIfNoCase Referer "^http://www\.website\.be/" acces_local=1
<FilesMatch ".(pdf|xls|doc|docx|xlsx)">
Deny from all
Allow from env=acces_local
</FilesMatch>

SetEnvIfNoCase Referer "^http://www\.website\.biz/" acces_local=1
<FilesMatch ".(pdf|xls|doc|docx|xlsx)">
Deny from all
Allow from env=acces_local
</FilesMatch>

Problem:

Some of our users on some workstation & browser can't access to the file it returns:

-> You don't have permission to access > sites/default/files/documents/xxxx.pdf
OR
-> IE6 block & say: Unable to download file or block (40%) > maybe in ie6 option ?

Thanks in advance,

C