MDADM: error trying to re-assemble RAID array

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I am trying to re-assemble an mdadm raid array I was using in ubuntu. I ran the command:

sudo mdadm --assemble /dev/md0 /dev/sda1 /dev/sdb1 /dev/sdc1 /dev/sdd1

While the command line responded positively, I received several dialogs stating "cannot obtain lock on media .hal-mtab".

The raid didn't seem to get re-assembled.

Anyone know how to hunt this down?