[rt-users] "could not load valid user"

[Chris Dunning]

I've been using RT 3.4.5 for some time now and with much success.  Today
I upgraded to the latest 3.6.1.  The web interface is looking good but I
can't get email piping to work - we make heavy use of that.

My alias file has this line:

helpdesk: "|/usr/local/rt/bin/rt-mailgate --queue 'General' --url
http://rt.bluenoteweb.com/"

Using 3.4.5 I did not have the "--queue 'General'" in there, it
automatically created the ticket in the General queue if nothing else
was specified.  After the upgrade it gave me an error about not being
able to find the queue, so I added that.  Now I am seeing this error in
the logs:

Dec 14 12:17:44 beethoven RT: RT could not load a valid user, and RT's
configuration does not allow for the creation of a new user for this
email (chris at bluenoteweb.com).  You might need to grant 'Everyone' the
right 'CreateTicket' for the queue General.
(/usr/local/rt/lib/RT/Interface/Email.pm:241)
Dec 14 12:17:44 beethoven RT: RT could not load a valid user, and RT's
configuration does not allow for the creation of a new user for your
email. (/usr/local/rt/lib/RT/Interface/Email.pm:241)
Dec 14 12:17:44 beethoven RT: Could not record email: Could not load a
valid user (/usr/local/rt/share/html/REST/1.0/NoAuth/mail-gateway:73)

The second error message is returned to the requester and copied to me. 
I have tried this using non-privileged users, email addresses that were
not previously in the database, and privileged users.  In all cases an
emailed message is returned with this same error.  I tried replying to a
ticket through the web interface and then replying to the reply - same
error.  The group "everybody" definitely has rights to "createticket" in
the general queue.  I have double and triple checked that setting.

I have looked through the wiki and the mailing list archives. 
Everything I've found I've tried and with no luck.  The rights are set
correctly.  We are not using LDAP or any external authentication.

What's the next step to try?