Can't Format Second HDD

Added 2nd HDD (Seagate Momentus XT ST750LX003 750GB). Installation seems fine, Mini recognizes drive.

When I try to format, using Mac OS Extended (Journaled), it begins, then fails with the following error:

Disk Erase failed

Disk Erase failed with the error:

File system formatter failed.

Partition information then shows the name as diskOs2 with the Mac OS Extended as the type.

I can change the number of partitions, but it still gives the same error when I try to format one of the partitions.

Any ideas appreciated.