My guess is that this is an Electronic Keying problem, which will generate the status code "73" on most PLC-based DeviceNet scanners.
Every device on a DeviceNet network has an Identity Object, which includes the Vendor, Device Type, Device Code, and Major/Minor firmware revisions.
Every different power or voltage rating of AC drives (at least in the A-B world) has a different Device Code. For example, the "20AC..." part number is a 400V rated drive, while "20AD" is a 480V rated drive.
The idea behind this is to be able to more precisely identify a device other than by its node number, for functions like automatic parameter download, and to decrease the probability that you could run the wrong motor just because somebody turned a node address dial a millimeter too far.
If you need to swap out drives of different voltage ratings and frame types without changing the DeviceNet Scanlist in the scanner, you can go un-check the Device Code checkbox in the Electronic Keying section of the DeviceNet Scanner's scanlist entry for that drive.