Users may receive the error message:
“Partition failed with the error: POSIX reports: The operation couldn’t be completed. Cannot allocate memory.”
when attempting to erase and format or partition external hard drives under Mac OS X 10.6.x (Snow Leopard).
Evidence suggests that this issue stems from a problem with Mac OS X 10.6.x’s framework, which has been blamed for a number of other issues including stalling mouse/keyboard input and more.
If your external hard drive (and your Mac) has a FireWire interface, try connecting it via that interface, then performing the format or partition operation.
Alternatively, if you have a Boot Camp installation on your computer, try booting into Windows then initializing the drive.