Moved Blog to Subdomain Issue with –Error 500 on main domain

Hello Support,

I moved my blog from https://vivbounty.com/petblog to subdomain https://cherishmypets.vivbounty.com

Now my error 404 page which used to work and is in my www folder (https://vivbounty.com) now does not work. I get Internal Error 500 message whenever a typo happens on main domain. Example:

https://vivbounty.com/natural displays fine
https://vivbounty.com/natrl displays Internal Server Error 500

I’m not sure if this is chmod or .htaccess problems.

Here is what is on my .htaccess

<IfModule mod_rewrite.c>
ErrorDocument 404 /vb_404.html
Options +FollowSymlinks
RewriteEngine On
RewriteBase /petblog/
RewriteRule ^index\.php$ – [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /petblog/index.php [L]
RewriteRule ^petblog/(.*) https://cherishmypets.vivbounty.com/$1 [R=301,NC]
</IfModule>

My blog is fine sitting happily on its subdomain but my main domain is not. Thank you for your kind assistance in advance,
VivBounty