.htaccess error

Hi. I installed by blog on my site a few months back and now i am trying to password protect some of my other directories of the site with .htaccess. During installation, wordpress wrote the following lines in my .htaccess file

RewriteEngine On
RewriteBase /blog/
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /blog/index.php [L]

The password protect doesnt work if these lines are there in the file. If I remove these files, the password protect does work but none of my pages on the blog open.

Does anyone have a workaround this problem? Any help is highly appritiated!!