Stretch Alpha 8 netinst fails

[Michael Owen <mowen1947@gmail.com>]

Installation fails installing the base system:

/lib/partman/choose_partition/60partition_tree/do_option: line 88

/lib/partman/active_choices/copy/choices: not found

I've tried different hard drives, both installing on a blank drive and a
selected partition and always the exact same error message. I tried the
main Alpha 8 and a daily build...same results.

Hardware is older core 2 duo on SATA drive, nothing esoteric. I've
installed many distros and never got anything like this. Alpha 7
installs fine.