Reason of your 500 error is: Redirect to non-URL
As you're missing leading slash in your matching pattern and target URL.
Use this rule to fix it:
Redirect 301 /includes/config.php /includes/index.php
Question
I tried the following lines in .htaccess file and put it in includes folder:
//301 Redirect Old File
RewriteEngine on
Redirect 301 includes/config.php includes/index.php
I want when any user opens this file using url that he/she must be redirect to includes/index.php file. But I got the 500 server error.
Solution
Reason of your 500 error is: Redirect to non-URL
As you're missing leading slash in your matching pattern and target URL.
Use this rule to fix it:
Redirect 301 /includes/config.php /includes/index.php
OTHER TIPS
try:
Redirect 301 /includes/config.php http://yoursite.com/includes/index.php
Although, if the htaccess is in the includes dir then you don't need /includes at all. The second url must also be full - as above.