Non standard port - non default instance

Hi all,
I'm trying to create a subscription for a merge replication on a sql
server mobile 2005 based application.
The publisher is on a intranet, listening on port 9091 and with a named
instance.
The merge agent is in a DMZ with port 9091 open for inbound/outbound TCP
traffic to the intranet.
Problem:
when I try to synchronize I receive the "SQL Server does not exists" error.
My subscription has the following setup:
Publisher = "ServerName\InstanceName";
PublisherNetwork = NetworkType.TcpIpSockets;
PublisherAddress = "10.xxx.xxx.xxx,9091";
PublisherDatabase = "DatabaseName";
PublisherSecurityMode = SecurityType.DBAuthentication;
PublisherLogin = "name";
PublisherPassword = "pwd";
name/pwd user has correct priviledges non publisher database.
I can connect via SQL Client to the database from the machine in DMZ.
In my (many) tries, I also created an alias on the DMZ client and used
that for the Publisher property at the subscriber.
Nothing worked.
I'm finishing options...
Cl@. ha scritto:

> Problem:
> when I try to synchronize I receive the "SQL Server does not exists" error.
I solved opening 1434 udp port.
Question is: why sql client can connect without 1434 port open and the
merge agent can't?