Getting this error
POSIX reports: The operation couldn’t be completed. Cannot allocate memory

possible solutions.....
Just ran into POSIX errors with my 1TB Seagate FreeAgent XTreme Media drive. I'm running MAC OS X 10.6.8.

I read through a lot of this thread and tried some solutions. Switching between USB and Firewire did not work. Booting into safe mode and trying Disk Utility did not work. I did not have access to a pre 10.6 machine but I did have access to a Windows 7.

 

**Luckily this was my Time Machine drive so I did not even attemp to copy files off of the drive. The drive seemed to mount ok. I could navigate the directories but I could not write to the disk. 

 

So this is what worked:

On windows Machine, formatting drive to NTFS in "Disk Management" application. Fist I had to delete the (HFS) volume and the create a new NTFS volume.

 

Then on the iMac, Formatting to HFS(journaled) using Disk Utility.

 

Disk seems to be fine again. I can read and write to it normally again.

 

Hope this is useful.

Probably the partition table is corrupt. When it does this, it becomes difficult to
unmount (actually it gets stuck in a loop trying to mount the file system, to no avail
because the file system is corrupt).

This procedure forces a dismount, but does not eject the drive.
This breaks the loop and allows erasing the partition table:

open terminal.app

note: I wrote these instructions were for a boot volume
with that condition (booting from the install DVD), so the
disk numbers are not going to be accurate. 

at the prompt:
diskutil list
(press enter)
that will give you the device name of your drive.
It most likely will be "disk0".

next command:
diskutil unmount force /dev/<disk_name>
example:
diskutil unmount force /dev/disk0

next command:
diskutil zeroDisk /dev/<disk_name>
example:
diskutil zeroDisk /dev/disk0
(press return)

After disk is zeroed, you may resume normal partitioning.
#

Bear in mind, since this is an external disk, the USB/ translation layer
may interfere with accessing the disk directly and foul up the procedure. 

Looking at the drive specs, it says it only supports use under windows,
whatever that means. Perhaps it requires a proprietary USB driver or something.
Some folks claim it works on a Mac though.
http://techpatio.com/2010/reviews/hp-simplesave-2tb-usb-launcher-mac-blue-led

The USB interface (inside the unit) might be hosed.
Sales poop says it has a two year warranty. If still in warranty, send it back.
Usage:  diskutil [quiet] <verb> <options>, where <verb> is as follows:

     list                  (List the partitions of a disk)
     info[rmation]         (Get information on a specific disk or partition)
     listFilesystems       (List file systems available for formatting)

     u[n]mount             (Unmount a single volume)
     unmountDisk           (Unmount an entire disk (all volumes))
     eject                 (Eject a disk)
     mount                 (Mount a single volume)
     mountDisk             (Mount an entire disk (all mountable volumes))

     enableJournal         (Enable HFS+ journaling on a mounted HFS+ volume)
     disableJournal        (Disable HFS+ journaling on a mounted HFS+ volume)
     moveJournal           (Move the HFS+ journal onto another volume)
     enableOwnership       (Treat as exact User/Group IDs for a mounted volume)
     disableOwnership      (Ignore on-disk User/Group IDs for a mounted volume)

     rename[Volume]        (Rename a volume)

     verifyVolume          (Verify the file system data structure of a volume)
     repairVolume          (Repair the file system data structure of a volume)

     verifyPermissions     (Verify the permissions of a Mac OS X volume)
     repairPermissions     (Repair the permissions of a Mac OS X volume)

     eraseDisk             (Erase an existing disk, removing all volumes)
     eraseVolume           (Erase an existing volume)
     eraseOptical          (Erase optical media (CD/RW, DVD/RW, etc.))
     zeroDisk              (Erase a disk, writing zeros to the media)
     randomDisk            (Erase a disk, writing random data to the media)
     secureErase             (Securely erase a disk or freespace on a volume)
     resizeVolume             (Resize a volume, increasing or decreasing its size)

     partitionDisk         ((re)Partition a disk, removing all volumes)
     splitPartition        (Split an existing partition into two or more)
     mergePartitions       (Combine two or more existing partitions into one)

     appleRAID <raidverb>  (Perform additional verbs related to AppleRAID)