"No input file specified" Error in WordPress

In my case it was the presence of a file named .user.ini

Just deleted it.

This is a problem with your .htaccess file.

The fix:

Update to the latest WordPress. There is a permalink bug in some installations.

Make sure Apache is configured properly for ModRewrite.

From Support: On Options > Permalinks, is a section "Optional". It's not SO optional. After upgrading it mentioned for category's index.php/file (I've got the PATHINFO permalinks), I don't want "files" so I altered that to index.php/ Now that I've changed to index.php/_/ (or leave it blank which gives the standard "Category" subpath), its all working again. Here is the Mod Rewrite file:

<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
</IfModule>