>disk remove_ownership <disk_id>
If that doesen't do it, then,
>disk assign <disk_id> -f
You also might need to go to advanced mode before issuing those commands. >priv set advanced.
>priv set will simply bring you back to normal mode.
Do you know where that disk came from?
I mean, if it's not a empty one and there is a part of aggregate in it, and you assign it to your filer, you will get a warning message. Aggregate in degraded mode, or something like that, so don't panic, you just have to destroy it then