I've just bought a new MacBook Pro with Mac OS X Lion.
The problem started when I tried to divide the hard disk into more than 3 partitions, so I erased the existing partition and tried to divide the hard disk using Disk Utility. So, I opened the "Partition" tab and chose "3 partitions" and when I hit "Apply" it says that "Couldn't unmount partition".
Can anyone please tell me how to fix that or how can I partition my hard disk?