XF 1.5 help, site down, something about install-lock.php "failed to open stream"?!


Well-known member
I was on my site having a PM conversation and whatnot when suddenly my site's home page went blank and I got this when attempting to access admin:

[HEADING=1]Server Error[/HEADING]
fopen(/var/www/vhosts/xx.net/httpdocs/internal_data/install-lock.php): failed to open stream: No such file or directory
[*]fopen() in XenForo/Install/Model/Install.php at line 367
[*]XenForo_Install_Model_Install->writeInstallLock() in XenForo/ControllerAdmin/Abstract.php at line 99
[*]XenForo_ControllerAdmin_Abstract->_assertInstallLocked() in XenForo/ControllerAdmin/Abstract.php at line 16
[*]XenForo_ControllerAdmin_Abstract->_preDispatchType() in XenForo/Controller.php at line 310
[*]XenForo_Controller->preDispatch() in XenForo/FrontController.php at line 368
[*]XenForo_FrontController->dispatch() in XenForo/FrontController.php at line 152
[*]XenForo_FrontController->run() in /var/www/vhosts/xx.net/httpdocs/admin.php at line 13

I have PHP 7.3.17 on Ubunto 16.04 and Apache. I don't recall ever getting this error before and I was just using the site as usual. The install-lock.php file exists and I even tried giving it full permissions, but nothing. Help!!