.htaccess kills

Apache/2.0.52: (CentOS)
PHP: 4.3.9
mod_rewrite: loaded
AllowOverride: “All” (the customer service said so)

I created a blank .htaccess in the root directory, then CHMOD to 666, specified the structure: “/%category%/%postname%”. But after clicking on the button “Update Permalink Structure”, my browser returns a “403 Forbidden”, and the whole site is down, I can only see an error page possibly set by my host.

But the .htaccess file can be updated successfully, because it became 205byte after that, and what has been written into it is (I added the “===” ) :

====================================
# BEGIN WordPress
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
</IfModule>

# END WordPress
====================================

As long as the .htaccess exists, my site is not available.

My wordpress can be viewed only when the .htaccess is a blank file(with any attribute) or doesn’t exist, or I use default permalinks.

Please someone help me. The host is very expensive….. 🙁

Thank you guys.