Comment 1 for bug 435290

Thanks for your report. This upload should fix it:

partman-iscsi (3) karmic; urgency=low

  * Change priority to standard to match overrides.
  * Stop checking disk-detect/iscsi/enable before deciding whether to offer
    an option in the partitioner, as that template doesn't exist any more.

 -- Colin Watson <email address hidden> Fri, 02 Oct 2009 13:37:20 +0100

In the meantime, as a workaround, you can boot with anna/choose_modules=partman-iscsi as a boot parameter, and select "login to iSCSI targets" in the driver choice menu it gives you after realising that there are no local disks.