You cannot upgrade from SNA Server 4.0 to Host Integration Server 2004 if you do not run the Host Integration Server 2004 Configuration Wizard (884172)

INTRODUCTION

When you upgrade from Microsoft SNA Server 4.0 to Microsoft Host Integration Server 2004, the Host Integration Server 2004 Setup program detects SNA Server 4.0 and tries to update the installed features and configuration settings. As part of this process, the Setup program must remove SNA Server 4.0. After the Setup program has finished copying the files, you may receive the following message.

Note You may still be prompted to restart your system, even though you stopped all SNA Server 4.0 services before you started the upgrade process. Microsoft Host Integration Server 2004 Installation Wizard

You must restart your system for the configuration changes made to Microsoft Host Integration Server 2004 to take effect. Click Yes to restart now or No if you plan to manually restart later. If you click Yes, the Setup program finishes. However, the upgrade process is not finished until the Host Integration Server 2004 Configuration Wizard runs. The Host Integration Server 2004 Configuration Wizard was not started because the system must restart. After the system restarts, the Configuration Wizard is not automatically started. The only SNA Server 4.0 services that are still installed are SnaBase, SnaDlcx or any link services, and SnaServer. If you start SNA Manager, the server has a "Status Unavailable" status.