hiding file extension with htacces gives Internal Server Error?

Hello,

I get
Failed to load resource: the server responded with a status of 500 (Internal Server Error)
on every single image, js file and css file. How can i fix this issue?

Options -MultiViews
RewriteEngine On

# To externally redirect /dir/foo.php to /dir/foo
RewriteCond %{THE_REQUEST} ^[A-Z]{3,}\s([^.]+)\.php [NC]
RewriteRule ^ %1 [R=301,NE,L]

RewriteRule ^knowledge-center/(\d+)(?:/.*)?$ knowledge-center-desc.php?id=$1 [QSA,L,NC]

# To internally forward /dir/foo to /dir/foo.php
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_FILENAME}.php -f
RewriteRule ^(.*?)/?$ $1.php [L]

ServerSignature Off

DirectoryIndex schedule.php