Uncaught exception Unsupported major.minor version 51.0.
At least a Java 1.7 is needed to start the JMS agent.
However, the JMS agent also needs the local User Interface to run under at least Java 1.7 or later.
To choose the Java version for the UserInterface to start with, edit the UCDJ.ini file (found in the User Interface/bin directory) and edit the [GLOBAL] section:
cmd="<path to java 1.7>\javaw" -Xmx1024m -Dsun.locale.foratasdefault=true com.uc4.ucdf.UCDialogFactory -U%User%
Restart the UserInterface and the the error will not show up anymore.