Béat,
I've successfully setup and configured the Web Client for intranet access.
I have created a subdomain under our publicly accessible domain: subdomain.publicdomain.com
I have setup one of the empty ports on the Sonicwall to accept connections from this new subdomain and pointed it to the extra NIC on the server which has a different IP from the rest of our network.
I have purchased a Security Certificate and installed it on the server so I no longer get the "untrusted website" screens in either IE or Firefox whether accessing from intranet or internet.
I can successfully enter the URL in a browser outside the network and I get the Dynamics GP login page. I login and that is when the problem starts.
It says Initializing Application in the lower right corner and then I get an Application Errors window that says:
An error occurred while initializing communication with the server.
I click the error and get:
[CrossDomainError]
Arguments: https://servername.int.internaldomain.com/RuntimeService/15132
Debugging resource strings are unavailable. Often the key and arguments provide sufficient information to diagnose the problem. See http://go.microsoft.com/fwlink/?linkid=106663&Version=5.1.41212.00&File=System.ServiceModel.dll&Key=CrossDomainError
I saw your response mentioned enabling cross-domain trusts, but when I go into Active Directory Domains and Trusts, I only have my internal domain showing and going through the New Trust Wizard, I am informed that the trust needs to be created on both domains. I'm not sure where to proceed from here.