cannot delete/unmount old boot volume

[cjoy]

I've carbon copied my vanilla install of Mac OS X (SL) onto a SSD and can boot using the latter without problems (also when removing the old drive).
Now I'd like to delete/partition the former startup volume, but DiskUtility wont let me. It fails to unmount the drive.

Any ideas on how to solve this issue are much appreciated.

edit:
system disk to the rescue - issue resolved

 

[mjsmke]

Are you sure you have booted from the new drive?

You could try booting from the install disk then use disk utility from there to erase the old volume.