[ic] SOAP access to interchange - logging on

[John1]

Sorry to keep answering my own posts, but I *really* am stuck this time. :-)

I have basic SOAP working, e.g. $Tag->session_name->result is correctly 
returning a session id, but

$Tag->userdb( $login_opt )->result refuses to log me on.

I have "SOAP_Control Tag/userdb always" in both my catalog.cfg and 
interchange.cfg, so I guess there must be something wrong with my logon.pl 
script (see below).  Please can anyone spot the problem - I have stared at 
it for hours and tried everything, but just get a "Service not found" error 
for the userdb call.

========================
#!/usr/bin/perl

use SOAP::Lite;

#no $cat parameter as catalog is
#accessed at root i.e.  www.mydomain.com/

my $host = 'www.mydomain.com';

my $Tag = SOAP::Lite
            -> uri("http://$host/Vend/SOAP")
            -> proxy("http://$host:7780/")
            -> on_debug (sub {print @_});

my $id = $Tag -> session_name ()->result;

my $proxy = "http://$host:7780/$id";
$Tag->proxy($proxy);

my $login_opt = {
    username => 'myusername',
    password => 'mypassword',
    function => 'login'
    };

my $ok = $Tag->userdb( $login_opt )->result;

========================
Output showing the error:
...
<SOAP-ENV:Body>
<SOAP-ENV:Fault>
<faultcode>SOAP-ENV:Client.NotFound</faultcode>
<faultstring>Service not found</faultstring>
</SOAP-ENV:Fault>
</SOAP-ENV:Body>
...