A copy of DefaultApp must run for each instance of a scripted WebObjects application.
The usage for DeDefaultAppfaultApp is
DefaultApp [applicationName] [-c] [-d DocumentRoot] [-v WebObjectsVersion] [-n InstanceNumber] [-p PortNumber] [-] ApplicationDirectory
Note for Windows NT users: The Web server uses the ApplicationDirectory argument to build URLs, so use forward slashes as opposed to a backslashes.