RewriteRule (contact.php -> contact) + 404 Redirection gives me always a 404 page - apache

Question

Recently i Modified my .htaccess file in my apache server. and this is the following code
RewriteEngine On
<IfModule mod_speling.c>
CheckSpelling On
</IfModule>
RewriteCond %{SCRIPT_FILENAME} !-d
RewriteCond %{SCRIPT_FILENAME} !-f
RewriteRule ^course/([^/.]+)$ course.php?name=$1 [QSA,L]
RewriteRule ^course/([^/.]+)/$ course.php?name=$1 [QSA,L]
RewriteRule ^about$ about.php [QSA,L]
RewriteRule ^about/$ about.php [QSA,L]
RewriteRule ^contact$ contact.php [QSA,L]
RewriteRule ^contact/$ contact.php [QSA,L]
RewriteRule ^downloads$ downloads.php [QSA,L]
RewriteRule ^downloads/$ downloads.php [QSA,L]
RewriteRule ^ errors/404.html [L,NC]
Now the Problem is
If I I enter the URL like http://localhost/about in my web browser it well always shows the custom 404.html
I think the problem is on the last line.
If i remove the last line it will works.
But I also want the 404 page. Like If the user enters http://localhost/SomeRandomString the 404 page show on this url.
I also tried ErrorDocument on .htaccess file but it will change the url
Is any solution for this problem.

Answer 1

Have your htaccess rules file in following way. Place it in your root directory, make sure to clear your browser cache before checking your URLs.
RewriteEngine On
<IfModule mod_speling.c>
CheckSpelling On
</IfModule>
##Rules that cover your uris starting with course here.
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_FILENAME} !-f
RewriteRule ^(course)/([^/.]+)/?$ $1.php?name=$2 [NC,QSA,L]
##Rules that cover your uris starting with about/contact/downloads here.
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_FILENAME} !-f
RewriteRule ^(about|contact|downloads)/?$ $1.php [NC,QSA,L]
##Rules that cover all uris which aren't matching any of the above conditions.
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_FILENAME} !-f
RewriteRule ^ errors/404.html [L,NC,QSA]