That means the ARX file isn’t load successful. You can try to load the ARX in AutoCAD.
How to “install” an ARX application?
simple, single file ARX application can be loaded just by mouse-dragging of the ARX file to a running AutoCAD window.
If you want to load your ARX application into every AutoCAD session, add its filename to your ACAD.RX file (use a text editor). Or – in a simpler way – use the StartUp Suite in the APPLOAD dialog. You can even just drag your ARX file from Windows Explorer to the Briefcase icon in the APPLOAD dialog.
Another way of loading an ARX file is the ARX command or the (arxload) LISP function.
The ARX you can find at where you installed them. Below is the list.
AutoCAD 2002 *15.arx
AutoCAD 2004~2006 *16.arx
AutoCAD 2007~2009 *17.arx
AutoCAD 2010~2011 *18.arx