How can I delete a subkey that has no USAGE assigned to it?

[stebe at mailbox.org]

Hi,

I have generated a new pub key with several subkeys following (1). While
generating one of the subkeys, just after gpg tells you to play around
with your mouse or do some keystrokes in the terminal, gpg output was: key
generation failed. To start generating this encryption subkey again, I
typed
gpg> quit
$ gpg2 --edit-key XXXXXXXX
[key/subkey listing]
gpg> addkey 
#once again, but I did't think of typing
pfkill gpg-agent 
#this time, as I had done at the beginning of key generation.

I could create the remaining subkey(s) but had to type in the passphrase
into pinentry every time.
When I had generated the last subkey, I realized that there was one subkey
that had
no USAGE assigned to it, precisely the one the generation of which failed.
(I really don't know why, I did a thousand keystrokes and painted a gimp
masterpiece in the meanwhile).

#I tried to use
key XXXXXXXX # where XXXXXXXX is the keyID of the subkey
delkey XXXXXXXX
#to get rid of it, but gpg still tells me I have to select at least one
key, so it's not the (sub)keyID I have to type in.

My assumption: I suppose the "N" in the explanation of the key and delkey
command refers to the USAGE:[letter], as I can't think of any other way of
referring to that key. USAGE, however, is blank. I couldn't find any
further details about it in the manpages.

Is there a way to delete this subkey? 

TIA

Stebe

(1)https://wiki.fsfe.org/Card_howtos/Card_with_subkeys_using_backups