Is my Boot DVD needed to clone HD with 10.8.2 Mac Pro (Early 2008)

No. To clone a Mountain Lion boot volume:

Clone Lion/Mountain Lion using Restore Option of Disk Utility

Boot to the Recovery HD:

Restart the computer and after the chime press and hold down the COMMAND and R keys until the menu screen appears. Alternatively, restart the computer and after the chime press and hold down the OPTION key until the boot manager screen appears. Select the Recovery HD and click on the downward pointing arrow button.

1. Select Disk Utility from the main menu then press the Continue

button.

2. Select the destination volume from the left side list.

3. Click on the Restore tab in the DU main window.

4. Check the box labeled Erase destination.

5. Select the destination volume from the left side list and drag it

to the Destination entry field.

6. Select the source volume from the left side list and drag it to

the Source entry field.

7. Double-check you got it right, then click on the Restore button.

Destination means the external backup drive. Source means the internal startup drive.

This is because Mountain Lion will not let you clone the boot volume as you could with Snow Leopard and earlier.

If you are cloning from one drive to another using Disk Utility from the Recovery HD, then there is no reason for that error to occur unless there is a problem with your AEBS connection.

Select the OS X volume and verify if the volume is Journaled. If not, then click on the Journal icon in the DU toolbar. But if this is not helping then download Carbon Copy Cloner 3.5.2 and use it to clone the drive. CCC doesn't require that you boot from the Recovery HD partition and it will happily clone a startup drive.