When you run IPSentry as an NT system service, you MUST be sure that the user under which IPSentry is running has rights to various network components being monitored. We recommend that IPSentry be run under the exact same account that is used to configure IPSentry.  If you configure IPSentry as Administrator but run it under Some Limited User... the security contexts will be incorrect and you will begin getting access denied errors, credential errors, and etc.

If you set IPSentry to run under the local system - it will run precisely as that "Local System"