Acronis TH 11 sees destination drive of successful clone but windows Vista does not - disappeared!

I use array of WD external Passport drives and usually do file/folder backups from one to another. Decided to try to cloning source to another PP drive as an extra backup, clone successful according to Acronis, clone visible in Acronis, can be seen to safely disconnect external drives in WD Smartware, but INVISIBLE in Windows Explorer. ????? So I can't see it to delete clone and just go back to full data backups.