Hi Adrian,
1.Netcam server, NCS X, is running or is it when NCS is running as a service?
2.is it when you try to start the web client http://localhost:8100 on the same computer that runs ncs or is from another computer on the LAN?
OK, I think this is the problem. Exit NCS or Stop the NCS Service. Go to the Task Manager and to the tab Processes. Look for Netcam studio processes. You probably have a process running. Kill that or these processes. Restart and enter the http again.
If this is the case go to the forum post and download the latest version Netcam Studio 1.5.6
-Henrik