Comment 6 for bug 945027

Same problem here, Ubuntu 12.04 64-bit on Macbook 4,1.
/var/log/syslog contains the error:

May 25 01:23:18 ubuntu ubiquity[13176]: Device free not found in os-prober output
May 25 01:23:18 ubuntu ubiquity[13176]: Device /dev/sda1 not found in os-prober output
May 25 01:23:18 ubuntu ubiquity[13176]: Device free not found in os-prober output
May 25 01:23:18 ubuntu ubiquity[13176]: Device free not found in os-prober output
May 25 01:23:18 ubuntu ubiquity[13176]: Traceback (most recent call last):
May 25 01:23:18 ubuntu ubiquity[13176]: File "/usr/lib/ubiquity/ubiquity/misc.py", line 203, in boot_device
May 25 01:23:18 ubuntu ubiquity[13176]: for part in p.partitions():
May 25 01:23:18 ubuntu ubiquity[13176]: File "/usr/lib/ubiquity/ubiquity/parted_server.py", line 206, in partitions
May 25 01:23:18 ubuntu ubiquity[13176]: self.open_dialog('PARTITIONS')
May 25 01:23:18 ubuntu ubiquity[13176]: File "/usr/lib/ubiquity/ubiquity/parted_server.py", line 135, in open_dialog
May 25 01:23:18 ubuntu ubiquity[13176]: self.outf = open(outfifo, 'r')
May 25 01:23:18 ubuntu ubiquity[13176]: IOError: [Errno 2] No such file or directory: '/var/lib/partman/outfifo'
May 25 01:23:18 ubuntu ubiquity[13176]:
May 25 01:23:18 ubuntu ubiquity[13176]: Traceback (most recent call last):
May 25 01:23:18 ubuntu ubiquity[13176]: File "/usr/lib/ubiquity/ubiquity/misc.py", line 203, in boot_device
May 25 01:23:18 ubuntu ubiquity[13176]: for part in p.partitions():
May 25 01:23:18 ubuntu ubiquity[13176]: File "/usr/lib/ubiquity/ubiquity/parted_server.py", line 206, in partitions
May 25 01:23:18 ubuntu ubiquity[13176]: self.open_dialog('PARTITIONS')
May 25 01:23:18 ubuntu ubiquity[13176]: File "/usr/lib/ubiquity/ubiquity/parted_server.py", line 137, in open_dialog
May 25 01:23:18 ubuntu ubiquity[13176]: self.error_handler()
May 25 01:23:18 ubuntu ubiquity[13176]: File "/usr/lib/ubiquity/ubiquity/parted_server.py", line 126, in error_handler
May 25 01:23:18 ubuntu ubiquity[13176]: raise PartedServerError(exception_type, message, options)
May 25 01:23:18 ubuntu ubiquity[13176]: PartedServerError: ('', '', [])
May 25 01:23:18 ubuntu ubiquity[13176]:
May 25 01:23:18 ubuntu ubiquity[13176]: debconffilter_done: ubi-partman (current: ubi-partman)
May 25 01:23:18 ubuntu ubiquity[13176]: dbfilter_handle_status: ('ubi-partman', 141)