You need to use bpexpdate with '-copy <copy_number>' :
bpexpdate: -backupid <backup id> -d <mm/dd/yyyy HH:MM:SS | 0 | infinity>
[-client <name>] [-copy <number>] [-force] [-nodelete] [-notimmediate]
[-M <master_server,...,master_server>]
Since your original post was for VAULT duplication - please elaborate on what is 'not working'?
Please post a screendump of the 'Choose Backups' tab as well as Duplication tab of your vault profile.