I see what you mean. And also, if you're making the change in the web.config, that should trigger an application restart anyway.
Something is preventing the pageSecurity object from being set. You could do a global text search for "pageSecurity" and find the code that sets it. That may be where the failure is happening.
Normally I would expect this to be caused by a missing security-related table, like Roles or something. But you said it was a full copy. You might want to double check.