Is there a setting that disables access to the 'THIS' scope from the Application.cfc in other pages in CFAdmin or something? My dev version of CF21 allows me to dump it on a regular cfm page, for example, but it isn't accessible on our new CF21 test server.

I'm not sure about your actual question, but I'd discourage you from accessing the this scope of application.cfc directly from code on a cfm page, or from anywhere really except code in that same application.cfc. What are you trying to references in there?

I agree, it is an ancient app that is being migrated and was setting some variables using THIS, so I'll probably just change the scope... But the inconsistency is pretty strange that it is accessible on one server and not the other.