Comment 8 for bug 813134

live-cd currently does not have partman plugins installed for cryptsetup / luks devices.

Partman has detected no partitions on the sdb, and total usable/resizable size of 0 bytes.

After choosing "parrallel to exsiting installation" ubiquity should have still presented you with the sreen to select a drive and/or define the resize split. Unfortunately, at this point partman probably defaulted to sdb as it is "bigger free" than the "resize of sda".

Installer generally allows the user to choose which partition to format and loose data on....

This will be improved for quantal. As the current plan is to include cryptsetup plugins, and we should be able to determine LUKS devices during the installation. Until then, LUKS disks will appear as opaque.