Hello, I am trying to erase only the free space on a drive. I go Tools > Drive wiper, select Free Space Only. When selecting the number of passes, if I select "1" then both hard drives are selectable, but the option "Wipe" to actually proceed is not selectable with either drive selected. If I instead select more than 1 pass, the drive I'm trying to erase free space on gets greyed out, and "Wipe" is still not selectable.