Using Lion's DU. Trying to erase a Sno Leopard partition on an external HD (to clone Lion to it via CCC). The external has not been problematic.

In DU, I select the external and select the Sno Leopard partition icon. Click erase. Get the message: "Volume erase failed with the error: POSIX reports: The operation couldn't be completed. Operation not permitted".

Before trying to erase, I started CCC cloning to the Snow Leopard partition. Then thought better of that and stopped the cloning after two minutes. Then tried to erase and got the failure message. Tried again to erase, and the same failure message recurs.

Ran DW on the recalcitrant Sno Leopard partition -- but in trying to erase the contents of that partition, got the same POSIX error.

So went to the partition map and deleted the snow Leopard partition and created a replacement partition of the same size. Then using CCC, cloned Lion to the newly created partition.

My external is a FW drive and is formatted as APM (not GUID) because I have a partition on it holding a clone of an older PPC Mac. Can boot from the newly created Lion partition.

Thanks for the heads-up.

"POSIX error: Operation not permitted: usually means that the disk could not be unmounted (ejected) for some reason. Use the Finder to eject the external disk by dragging it to the Trash. It should disappear from your desktop but still be seen in Disk Utility, and you should then be able to erase it.

When I highlighted the Sno Leopard partition and clicked on "Erase", that partition dismounted. Then I got the POSIX error message. Using a menu command in DU, I could remount that partition. And I tried to erase it again with the same result.

As I reported, I then deleted that partition and recreated it using DU. I cloned Lion to it from the computer's HD using CCC. Just to test, I then used DU to erase that partition. This time DU succeeded in erasing it. So I again cloned Lion from the computer's HD to that partition.

Whatever the original glitch was, it was not DU's inability to unmount the Sno Leopard partition.

Weird. That's bizarre. I don't think I've ever seen that particular problem. Glad you got it worked out, but I'd love to have a better understanding of what the original problem was.