Trying to open a file in GNOME Commander (1.2.7 Ubuntu 9.04) produces the following (not very helpful) error message:-

No default application found for the MIME type application/x-glade.
Open the "File types and programs" page in the Control Center to add one.

Trying to change the default application in Properties by clicking the Change button has no effect (it just changes colour).

The default is set in Nautilus, and works there.