Demo listener on linux throwing error

Hi,

I am using DemoListener.java built into Demo.jar file. When I use this jar file on linux, getting following error..

java.lang.UnsupportedClassVersionError: soapui/demo/DemoListener : Unsupported major.minor version 51.0
at java.lang.ClassLoader.defineClass1(Native Method)
at java.lang.ClassLoader.defineClassCond(ClassLoader.java:631)
at java.lang.ClassLoader.defineClass(ClassLoader.java:615)
at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:141)
at java.net.URLClassLoader.defineClass(URLClassLoader.java:283)
at java.net.URLClassLoader.access$000(URLClassLoader.java:58)
at java.net.URLClassLoader$1.run(URLClassLoader.java:197)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:190)
at java.lang.ClassLoader.loadClass(ClassLoader.java:306)
at java.lang.ClassLoader.loadClass(ClassLoader.java:295)
at groovy.lang.GroovyClassLoader.loadClass(GroovyClassLoader.java:696)
at groovy.lang.GroovyClassLoader.loadClass(GroovyClassLoader.java:793)
at java.lang.ClassLoader.loadClass(ClassLoader.java:295)
at java.lang.ClassLoader.loadClass(ClassLoader.java:247)
at java.lang.Class.forName0(Native Method)
at java.lang.Class.forName(Class.java:247)
at com.eviware.soapui.support.scripting.listeners.AbstractScriptListener.syncClass(SourceFile:35)

Linux has java version 1.7.0_07 and demo.jar file is built on 1.6.0_35. Linux is 64 bit Ubuntu and demo.jar file is built on windows.

thanks,
shyam