Using Data Centre/Center Expert and adding an APC ATS switch, even though the configuration was correct, FTP was enabled and the relevant settings set for SNMP for the relevant IP addresses the following error is observed in the Data Centre Expert “Device status may be inaccurate due to attempt to transfer DDF failed”.
After much research https://community.exchange.se.com/t5/EcoStruxure-IT-forum/Transfer-Of-A-Device-Definition-File-DDF-Failed/td-p/206111 no settings changes could resolve the issue.
The solution is to upgrade the firmware of the ATS. Firstly download from: https://www.apc.com/shop/us/en/tools/software-firmware/ then download the latest version, at the time of writing for me this was AP44XX Series Rack ATS Unit Firmware Revision 6.5.6 (SFATS4G656).
Download and run the tool to upgrade the ATS firmware.
Once complete from within DCE run a “Request Device Scan” you should find that the DDF file is downloaded correctly and the error should disapear.