version) suddenly throwing "Java Exception" errors or failing to open entirely, you aren't alone. This classic utility has become increasingly finicky with modern Java Runtime Environments (JRE).
Follow this exact workflow. Deviations—especially using the wrong Java version—will cause failure.
The safest and most effective way to run the tool is to use an older, portable version of Java specifically for this app, rather than downgrading your entire system's Java. Ubiquiti Community Download a Legacy JRE/JDK
The legacy Discovery Tool (specifically version ) is a staple in many tech toolkits because of its lightweight nature, but it was built for an older era of Java. On modern Windows 10 systems, getting it to run can be a headache.
So your full command: %JAVA_HOME%\java.exe -XX:+UseParallelGC -Djava.net.preferIPv4Stack=true -jar UBNT_Discovery_Tool_v2.5.1.jar