I think that's because you have to select Window PE bootable disk in Step 1 of 5: Installer Operating System.
With DS 6.9 SP3 the Wizard is slightly different:
1) Open Boot Disk creator
2) Right Click your WinPE in the Configuration List select Create Partition installer
3) Select "Bootable installer Disk"
4) Select "Create a Hidden Winpe 2.1 partition", click Next