Error on an application that was working fine, and hadn't changed

2 = Cannot use a scalar value as an array
/opt/NetMake/v9-php73/wwwroot/scriptcase/devel/compat/compat.inc.php 902

Anyone know what this means - or why it’s suddenly come up?
My apps are pretty simple and only used ‘in house’ so this is a real pain - I even tried restoring to an earlier saved copy - and it’s still doing the same error…

php version?
did you change it?
php 7.4 doesn’t work in SC yet.