zobacz linki:

http://www.drupal.pl/node/2116
http://drupal.org/node/187912
http://www.drupal.pl/node/398

sprawdź opis na:
http://drupal.pl/node/2586?page=1#comment-9723

czyli:

usunąć z pliku htacces fragmenty kodu:

# Serve gzip compressed CSS files if they exist and the client
accepts gzip.
RewriteCond %{HTTP:Accept-encoding} gzip
RewriteCond %{REQUEST_FILENAME}.gz -s
RewriteRule ^(.*).css $1.css.gz [QSA]

# Serve gzip compressed JS files if they exist and the client
accepts gzip.
RewriteCond %{HTTP:Accept-encoding} gzip
RewriteCond %{REQUEST_FILENAME}.gz -s
RewriteRule ^(.*).js $1.js.gz [QSA]

# Serve correct content types, and prevent mod_deflate double gzip.
RewriteRule .css.gz$ - [T=text/css,E=no-gzip:1]
RewriteRule .js.gz$ - [T=text/javascript,E=no-gzip:1]

FilesMatch "(.js.gz|.css.gz)$">
# Serve correct encoding type.
Header append Content-Encoding gzip
# Force proxies to cache gzipped & non-gzipped css/js files
separately.
Header append Vary Accept-Encoding