Wordress & Plugin Update 404 Error Message

When logging into my Dashboard I have the following messages:

An updated version of WordPress is available.

The following plugins have new versions available.

However, when I click on “Update Now” to get the latest WP version I get the following:

https://www.SITENAME/wp-admin/update-core.php?action=do-core-upgrade and on the page: Home→404 Page not found

When clicking Update Plugin I get: https://www.SITENAME/wp-admin/update-core.php?action=do-plugin-upgrade and on the page: Home→404 Page not found

I have disabled all my plugins and then tried to install the latest WP version, but still get the same error. Any other suggestions would be appreciated.