Warning: require(/wp-admin/wp-blog-header.php): failed to open stream: No such file or directory in /wp-admin/index.php on line 17

[admin]

I found this error in my wordpress site

Warning: require(/home/cjstech/public_html/wp-admin/wp-blog-header.php): failed to open stream: No such file or directory in /home/cjstech/public_html/wp-admin/index.php on line 17

I will gladly appreciate anyone who has some knowledge about how to fix this issue.

Thanks!