Partition issue, couldn't unmount disk (error)

It sounds like you're trying to partition the drive. You can't do that while booted from it. You would have to boot from another device, such as a Time Machine backup drive, Lion Internet Recovery, or a USB drive prepared with Lion Recovery Disk Assistant.

In DU on the partition tab highlight the last partition and click the Minus Sign. Then expand the first partition to include the whole drive (bottom right hand corner). Then go to the Erase Tab and select the new expanded partition then click erase.

NOTE:

You must be booting the computer from the Recovery HD partition, a USB stick with the Recovery HD partition files on it, Internet Recovery system or a OS X install DVD to do this.

You can not select the complete, physical, drive while booting the computer form any of it partitions.

Boot from another device as suggested above.

Post a screen shot of the Disk Utility window with the partition tab shown.

Describe exactly, step by step, what you did and what happened, including the complete text of any error message you saw.

For the second and last time, you can't partition the drive while booted from one of its partitions. You must boot from another physical device.

When asked for an exact description of what you're trying to do, you posted only a screenshot that shows an attempt to erase a volume, and an error message different from the one you've been reporting. That conflicts with your verbal description. Every message from you in this thread says something different. When you can come up with an exact, complete, consistent description of the problem, please post it.

Linc you can change, resize, and add partitions when booted into the OS or from the R-HD or from booting from an install disc using Disk Utility.

You have to use the resize arrow, in red bottom right corner, to drag the existing partition up, resizing it, then create a new partition from the space left over.

You can't use the Partition drop down, in Yellow.