Sé que hay conflicto de versiones. Sólo quiero que alguien me diga cómo resolverlo. En la publicación anterior de stackoverflow nadie dice la solución.

Versiones: Ubuntu: 12.04.1 LTS java: 1.6.0_24 (OpenJDK) javac: 1.7.0_07 (OpenJDK)

haider@haider-desktop:~/Documents/projects/java-projects/mytestapp$ play
[info] Loading project definition from /home/haider/Documents/projects/java-projects/mytestapp/project
[info] Set current project to mytestapp (in build file:/home/haider/Documents/projects/java-projects/mytestapp/)
       _            _ 
 _ __ | | __ _ _  _| |
| '_ \| |/ _' | || |_|
|  __/|_|\____|\__ (_)
|_|            |__/ 

play! 2.0.4, http://www.playframework.org

> Type "help play" or "license" for more information.
> Type "exit" or use Ctrl+D to leave this console.

[mytestapp] $ run

--- (Running the application from SBT, auto-reloading is enabled) ---
[info] play - Listening for HTTP on port 9000...

(Server started, use Ctrl+D to stop and go back to the console...)

[info] Compiling 5 Scala sources and 2 Java sources to /home/haider/Documents/projects/libraries/play-2.0.4/samples/java/helloworld/target/scala-2.9.1/classes...
[warn] Problem processing dependencies of source /home/haider/Documents/projects/libraries/play-2.0.4/samples/java/helloworld/target/scala-2.9.1/src_managed/main/controllers/routes.java : java.lang.UnsupportedClassVersionError: controllers/routes : Unsupported major.minor version 51.0
[warn] Problem processing dependencies of source /home/haider/Documents/projects/libraries/play-2.0.4/samples/java/helloworld/target/scala-2.9.1/src_managed/main/controllers/routes.java : java.lang.UnsupportedClassVersionError: controllers/routes$javascript : Unsupported major.minor version 51.0
[warn] Problem processing dependencies of source /home/haider/Documents/projects/libraries/play-2.0.4/samples/java/helloworld/target/scala-2.9.1/src_managed/main/controllers/routes.java : java.lang.UnsupportedClassVersionError: controllers/routes : Unsupported major.minor version 51.0
[warn] Problem processing dependencies of source /home/haider/Documents/projects/libraries/play-2.0.4/samples/java/helloworld/target/scala-2.9.1/src_managed/main/controllers/routes.java : java.lang.UnsupportedClassVersionError: controllers/routes$ref : Unsupported major.minor version 51.0
[warn] Problem processing dependencies of source /home/haider/Documents/projects/libraries/play-2.0.4/samples/java/helloworld/target/scala-2.9.1/src_managed/main/controllers/routes.java : java.lang.UnsupportedClassVersionError: controllers/routes$javascript : Unsupported major.minor version 51.0
[warn] Problem processing dependencies of source /home/haider/Documents/projects/libraries/play-2.0.4/samples/java/helloworld/target/scala-2.9.1/src_managed/main/controllers/routes.java : java.lang.UnsupportedClassVersionError: controllers/routes : Unsupported major.minor version 51.0
[warn] Problem processing dependencies of source /home/haider/Documents/projects/libraries/play-2.0.4/samples/java/helloworld/target/scala-2.9.1/src_managed/main/controllers/routes.java : java.lang.UnsupportedClassVersionError: controllers/routes$ref : Unsupported major.minor version 51.0
[warn] Error reading API from class file : java.lang.UnsupportedClassVersionError: controllers/routes$javascript : Unsupported major.minor version 51.0
[warn] Error reading API from class file : java.lang.UnsupportedClassVersionError: controllers/routes : Unsupported major.minor version 51.0
[warn] Error reading API from class file : java.lang.UnsupportedClassVersionError: controllers/routes$ref : Unsupported major.minor version 51.0
[warn] Problem processing dependencies of source /home/haider/Documents/projects/libraries/play-2.0.4/samples/java/helloworld/app/controllers/Application.java : java.lang.UnsupportedClassVersionError: controllers/Application$Hello : Unsupported major.minor version 51.0
[warn] Problem processing dependencies of source /home/haider/Documents/projects/libraries/play-2.0.4/samples/java/helloworld/app/controllers/Application.java : java.lang.UnsupportedClassVersionError: controllers/Application : Unsupported major.minor version 51.0
[warn] Problem processing dependencies of source /home/haider/Documents/projects/libraries/play-2.0.4/samples/java/helloworld/app/controllers/Application.java : java.lang.UnsupportedClassVersionError: controllers/Application$Hello : Unsupported major.minor version 51.0
[warn] Problem processing dependencies of source /home/haider/Documents/projects/libraries/play-2.0.4/samples/java/helloworld/app/controllers/Application.java : java.lang.UnsupportedClassVersionError: controllers/Application : Unsupported major.minor version 51.0
[warn] Error reading API from class file : java.lang.UnsupportedClassVersionError: controllers/Application$Hello : Unsupported major.minor version 51.0
[warn] Error reading API from class file : java.lang.UnsupportedClassVersionError: controllers/Application : Unsupported major.minor version 51.0
[info] play - Application started (Dev)