Right, http://xxx.org/admin/content/types/foobar gives you a http://xxx.org/admin/content/types page when a "foobar" content type has not been defined or a module responsible for it is disabled/broken.
ah, very interesting.
So, does the "audio" content type appear in your list of types in the http://xxx.org/admin/content/types page or not?
If it exists, is "audio" its exact machine-readable name, and does its link lead exactly to http://xxx.org/admin/content/types/audio ?
Yes, it exists and that's the link. I chose that as an example, but this problem exists for ALL content types which I can click 'edit' on from /admin/content/types including:
http://xxx.org/admin/content/types/page
The live site works fine--all nodes appear to be in working order. I am still investigating the mod code. Slowly... :(
Fred