I have a WD Ext HDD 1021 USB connected, 3 Terabyte Hard drive.
After a little time, Defraggler will sense that it is connected (though not usually immediately, as for hard drives.
Any time that I try to analyze the drive for fragmentation, Defraggler returns the message "Analysis failed".
I am using the latest version of Defraggler. I am running Windows XP, not Windows 7.