Hello Nick,
I suspect that Joomla forgot to copy all the files, so you have a partial installation.
You have to re-install the package again in order to fix your issue.
After logging in you will get the error, but you'll be able to directly access admin pages.
Please enter the following URL in the address bar:
www.yourdomain.com/administrator/index.php?option=com_installer
You'll see the extension manager page, please install the latest version again in order to copy all the files.
Davide Tampellini
Developer and Support Staff
🇮🇹Italian: native 🇬🇧English: good • 🕐 My time zone is Europe / Rome (UTC +1)
Please keep in mind my timezone and cultural differences when reading my replies. Thank you!