PPA upload rejected, signature not recognized?

[Andrea Ratto]

Hi, I am trying to use the new PPA service, but my uploaded files get
this error:

Rejected:
PPA uploads must be signed by an 'ubuntero'.

I am building the package with "debuild -S -sa"
My gpg key is correctly set on launchpad, and the .changes file is
correcly signed using that key.

####
andrea at andrea-laptop:~/tmp$ LANG=en gpg --verify kvm_53
+dfsg-0ubuntu1~ppa1_source.changes 
gpg: Signature made Wed Nov 28 20:34:52 2007 CET using DSA key ID
D7853F21
gpg: Good signature from "Andrea Ratto <andrearatto at yahoo.it>"
gpg:                 aka "Andrea Ratto <ratto.andrea at educ.di.unito.it>"
gpg:                 aka "Andrea Ratto <andrearatto_liste at yahoo.it>"
####

Any clue?
Thanks