Proof of email ownership

[Simon Josefsson]

Werner Koch <wk at gnupg.org> writes:

> To create a signature on an email (or any other data) you would use:
>
>   gpg -s -Npka-address at gnupg.org=werner at example.org foo

I get this:

jas at latte:~$ gpg -s -Npka-address at gnupg.org=jas at extundo.com foo

You need a passphrase to unlock the secret key for
user: “Simon Josefsson <simon at josefsson.org>”
1280-bit RSA key, ID B565716F, created 2002-05-05

gpg: can't put notation data into v3 (PGP 2.x style) signatures
jas at latte:~$

Is my key unusable with this scheme?