Please make sure that the IIS port is listening on the same port as configured in the server.conf in BASE_URL-parameter and that this port is not only open but also different to the one set for EXTERNAL_WEB_PORT configured in the same file and also in the workers.properties-file.
Also check the ISAPI:
1. Start | Setting | Control Panel | Administrator tools | IIS Manager 2. Click on the “(local computer)” | Web Services Extension 3. Check to see “All Unknown ISAPI Extensions” has “Allowed” status. If not, the redirector isapi will not execute and as a result, requests will not get to ITG server.
If all fails, please let's have more information about the configuration of the IIS-server and we'll try to assist further.