I created a sub-file named blog in my site's server. access the blog url is:
http://example.com/blog or http://example.com/blog/?p=123
when i checked Post name checkbox item http://www.example.com/blog/index.php/sample-post/ in the Permalink Settings part. when i access post. it shows not found. when i unenabled the url rewrite. when view all the post,all are ok.

my server supports the url rewrite.then i created .htaccess(644). put it into blog file and put code:

HTML Code:
# BEGIN WordPress
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /blog
RewriteRule ^index\.php$ - [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
# END WordPress
it still can't work. why?