are you pinging LAN or WAN computers? In case of slow networks the "red" status could be shown because a remote computer didn't reply to the ping request with the the maximum timeout period.
The timeout value can be adjusted via Tools \ Options \ Per Configuration Settings \ Registered Computers Status Check \ Scan Timeout
Should you continue to experience the problem, please email to support@. Please ZIP and attach content of the following folder:
%USERPROFILE%\Application Data\SmartCode Solutions\VNC Manager\
Kindest Regards,SmartCode Solutions Support