Problems when Updating to latest version 3.5.1

I am trying to complete the upgrade to version 3.5.1 and I am now running the last step: 3 Run The Update Wizard on this page: https://docs.expressionengine.com/latest/installation/update.html#

I successfully completed all prior steps.

When trying to execute the admin.php or to run the system directory I get: The www.olmcfssp.org page isn’t working

www.olmcfssp.org is currently unable to handle this request. HTTP ERROR 500

So I get this error when trying to execute these 2 links: http://www.olmcfssp.org/admin.php and http://www.olmcfssp.org/system/index.php

Can you please assist with what is happening with your product upgrade?

Thanks,

Greg