Netcam Studio 1.5.2 client won't start

Hmmmm, after server reboot we lost all ability to connect to IP cameras, still investigating. Cameras can connect via other tools.

NCS use ports 8100, 8120 and 8124. These ports cannot be used by another application. Check that.

netcam studio loading client, it reports no category found, AND YOU have found a possible solution? What is that?

I assume you are running Netcam Studio version 1.9.5.
This problem seems to be with the graphical interface and after a Windows update. Test the following:
Stop Netcam Studio.
-go to C:\Users%username%\AppData\Local\Moonware and delete all.
-go to C:\Users%username%\AppData\Local\Moonware_Studios and delete all.
-go to C:\Users%username%\AppData\Roaming\Moonware_Studios and delete all.
Start Netcam Studio again.

Is the problem still there it’s probably a damaged configuration file. A clean installation usually solves the problem. More info here How to make a clean installation of Netcam Studio