Disconnect everything else on the USB bus, and make sure you have enough power on USB.
Connect the configuration to another system running Linux or Windows or otherwise, and see if it works there.
Failing that, it appears either your disk or your USB bridge is not working correctly, or your disk is incompatible.
Thank you @MrHofman. I had a setup with 2 dock stations and 2 HDDs (my TimeCapsule had crashed and I needed to recover its content disassembling the "box"). I disconnected everything. I restarted the computer., I swithched the USB ports in which I had connected the dock stations; I swithched the HDDs from dock stations, and voilà, the system allowed me to format the "recovery" HDD. Sometimes the "simplest" solutions work...
@Linc Davis: prior to the fix described above, when trying to partition, same thing would occur : "can't open link / disk" error message. But now it seems to be working fine. Thank you anyway!