Unable to partition or erase ext drive

[uvex]

I initally tried to erase a 200gb external, but it froze up disk utility...so I had to force quit it. So I rebooted and tried it again, but now when I try to erase or partition it gives this error...

Disk Erase Failed
Disk Erase failed with the error:

Unknown error: -20

anyone know ehat I can do to get this thing erased and partitioned?

[JDar]

Others may help you more if you'll post what machine and the OS you are using, but a generic thing to check assuming you might be using OS X is the permissions set on the external disk (Get Info) and also try booting from Install Disk One and starting the Disk Utility from there, sort of doing an end run around your system. Might help, might not. Good luck!