Troubleshooting should start with reviewing the log files and the Readme file. Listed below are common problems and what the likely cause is:

Connection Attempt Failure. Unable to establish WMI connection. The remote server machine does not exist or is unavailable
This is a valid alert for a server being unavailable. You should investigate why the server is unreachable. It may be that the server has rebooted; a network problem; or firewall issues etc. 

Connection Attempt Failure. Unable to establish WMI connection. Permission denied
The server was reachable but the user account you are running Winmonitor with does not have permission to perform a WMI query of it. Either allow this permission to the remote host, or make the account an administrator on the host.

Failed to send alert via email. Err Number= -2147220973. Error description=The transport failed to connect to the server.
Winmonitor tried to send an email alert but could not contact the smtprelayserver defined in the .ini file. Check your firewall configuration, routing, and make sure you can telnet on port 25 to the email server.

Failed to send alert via email. Error description=The server rejected one or more recipient addresses. The server response was: 550 5.7.1 Unable to relay for sysadmin@yourdomain.com
The mail server does not allow relaying to this destination domain. Ensure that the account you are running winmonitor with has permission to relay email through this email server.
If trying to relay via Exchange Server please refer to to Microsoft Article KB895853 for guidance.