Since Dominion KVM server applet is not signed the JRE will block the app by default. The solution is to add url to Raritan KVM server to the exception list.
First, make sure that you open correct (the latest) Java Control Panel, this is especially important if you happen to have more than one JRE/JDK on your machine, because you won’t find the “Exception Site List” in older Java Control Panel. In my case (Windows7, x64) the best approach is to manually find the executable:
C:\Program Files (x86)\Java\jre7\bin\javacpl.exe
Then check the version:
Add url to exception list: - Done!