Note that from Cycle 8 the appropriate version of Java is automatically included in the OT download package. OT Web Start is not supported anymore starting from Cycle 8.
There was a bug in Java 9 which prevents the Web Start version of the OT from opening when you try to run it. The only solution is to ensure that you have Java 8 on your system and use it to run the OT.
The download stops with an Application Error with the reason: factory already defined. In the details you will get the following exception:
java.lang.Error: factory already defined
at java.base/java.net.URL.setURLStreamHandlerFactory(Unknown Source)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.base/java.lang.reflect.Method.invoke(Unknown Source)
at firstname.lastname@example.org/com.sun.javaws.Launcher.executeApplication(Unknown Source)
at email@example.com/com.sun.javaws.Launcher.executeMainClass(Unknown Source)
at firstname.lastname@example.org/com.sun.javaws.Launcher.doLaunchApp(Unknown Source)
at email@example.com/com.sun.javaws.Launcher.run(Unknown Source)
at java.base/java.lang.Thread.run(Unknown Source)
You can check which version of Java you have by typing "java -version" at the command line, as described in the OT Troubleshooting instructions at http://almascience.org/proposing/observing-tool/troubleshooting.
It is possible that this bug has now been fixed and we would appreciate any user feedback on this issue.