You need to clean this drive and let the S/W RAID rebuild the array again.
After you plugged the drive back to your DSS V6, go to DSS V6 webgui -> Setup -> S/W RAID -> MDx and in the "Manager" frame set the following flags to it:
F - set faulty
R - hot remove
then press "apply".
After that go to DSS V6 webgui -> Setup -> S/W RAID -> "Create new S/W RAID unit" select this hard drive and add it to your S/W RAID as "spare for "MDx". Now let the S/W RAID rebuild the array.