PHP error when upgrading to 2.7 from 2.5

Our site went down after Dreamhost upgraded our PHP to 7.3. I tried to install 2.7 but keep getting this message:

Warning : Use of undefined constant WEB_RELATIVE_THEME - assumed ‘WEB_RELATIVE_THEME’ (this will throw an Error in a future version of PHP) in /home/XXXXXX/XXXXXXX/admin/index.php on line 22

Warning : Use of undefined constant WEB_RELATIVE_VIEW_SCRIPTS - assumed ‘WEB_RELATIVE_VIEW_SCRIPTS’ (this will throw an Error in a future version of PHP) in /home/XXXXXX/XXXXXXX/application/libraries/Omeka/Controller/Plugin/ViewScripts.php on line 159

I was able to roll back the PHP version to 7.1 (the latest version that made all the error messages go away). However, now the Admin side looks like this:
VHSDashboard

Those complains about WEB_RELATIVE_THEME are a problem no matter what version of PHP you’re using.

They would point, most obviously at least, to an issue with the “bootstrap.php” file for your site. Have you edited it at all? That file sets the “WEB_RELATIVE” constants the error messages mentioned, and if they’re not set, things aren’t going to work properly.

This isn’t a common error… I almost want to say you have a bootstrap.php file from an older version of Omeka than the rest of your installation. If you tried to do an upgrade recently, perhaps you missed some files?

Thank you! That was the problem. When I upgraded, I forgot to copy over the more current hidden files (never upgrade Omeka when jetlagged!). Everything looks good now.