It seems the installation error is caused by the ubiquity migration assistant. With the migration assistant disabled, I am able to install the natty desktop i386 without any problems. The ubiquity migration assistant bug occurs still with today's build.
This issue is also mentioned in https://bugs.launchpad.net/ubuntu/+source/ubiquity/+bug/570845 ** Summary changed: - ubiquity tries to mount not selected Linux partitions to target directory + ubiquity migration assistant did not unmount other Linux volumes -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/689816 Title: ubiquity migration assistant did not unmount other Linux volumes -- ubuntu-bugs mailing list [email protected] https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
