wbadmin wbadmin delete systemstatebackup returns no system state backups were found

I have server 2012 R2 running as a VM under Hyper-V. I can run a system state backup to D: drive which is internal drive on the VM. When I run wbadmin get version out put looks normal showing a number of backups.  When I run wbadmin delete systemstatebackup -backuptarget:D: -keepversions:1 or variations such as wbadmin delete systemstatebackup -keepversions:1 or wbadmin delete systemstatebackup -backuptarget:D -keepversions:1 it gives the following:

Enumerating system state backups...
ERROR - No system state backups were found.
This command can be used to delete backups that only contain the system state.

Any suggestions would be great.

Thank you