[LibGDx][Android] Conversion to Dalvik format failed with error 1

hello guys … i’m having this error now and it is really confusing me
i have tried to clean project , stop auto build clean … etc but still not working

the full error code :


2014-05-18 02:39:24 - SuperRace-android] Dx 1 error; aborting
[2014-05-18 02:39:24 - SuperRace-android] Conversion to Dalvik format failed with error 1
[2014-05-18 02:40:22 - SuperRace-android] Dx 
UNEXPECTED TOP-LEVEL EXCEPTION:
java.lang.IllegalArgumentException: already added: Lnet/dermetfan/utils/libgdx/box2d/Chain$DefShapeBuilder;
	at com.android.dx.dex.file.ClassDefsSection.add(ClassDefsSection.java:122)
	at com.android.dx.dex.file.DexFile.add(DexFile.java:161)
	at com.android.dx.command.dexer.Main.processClass(Main.java:685)
	at com.android.dx.command.dexer.Main.processFileBytes(Main.java:634)
	at com.android.dx.command.dexer.Main.access$600(Main.java:78)
	at com.android.dx.command.dexer.Main$1.processFileBytes(Main.java:572)
	at com.android.dx.cf.direct.ClassPathOpener.processArchive(ClassPathOpener.java:284)
	at com.android.dx.cf.direct.ClassPathOpener.processOne(ClassPathOpener.java:166)
	at com.android.dx.cf.direct.ClassPathOpener.processDirectory(ClassPathOpener.java:229)
	at com.android.dx.cf.direct.ClassPathOpener.processOne(ClassPathOpener.java:158)
	at com.android.dx.cf.direct.ClassPathOpener.processDirectory(ClassPathOpener.java:229)
	at com.android.dx.cf.direct.ClassPathOpener.processOne(ClassPathOpener.java:158)
	at com.android.dx.cf.direct.ClassPathOpener.process(ClassPathOpener.java:144)
	at com.android.dx.command.dexer.Main.processOne(Main.java:596)
	at com.android.dx.command.dexer.Main.processAllFiles(Main.java:498)
	at com.android.dx.command.dexer.Main.runMonoDex(Main.java:264)
	at com.android.dx.command.dexer.Main.run(Main.java:230)
	at sun.reflect.GeneratedMethodAccessor62.invoke(Unknown Source)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
	at java.lang.reflect.Method.invoke(Unknown Source)
	at com.android.ide.eclipse.adt.internal.build.DexWrapper.run(DexWrapper.java:187)
	at com.android.ide.eclipse.adt.internal.build.BuildHelper.executeDx(BuildHelper.java:813)
	at com.android.ide.eclipse.adt.internal.build.builders.PostCompilerBuilder.build(PostCompilerBuilder.java:597)
	at org.eclipse.core.internal.events.BuildManager$2.run(BuildManager.java:733)
	at org.eclipse.core.runtime.SafeRunner.run(SafeRunner.java:42)
	at org.eclipse.core.internal.events.BuildManager.basicBuild(BuildManager.java:206)
	at org.eclipse.core.internal.events.BuildManager.basicBuild(BuildManager.java:328)
	at org.eclipse.core.internal.events.BuildManager.build(BuildManager.java:403)
	at org.eclipse.core.internal.resources.Project$1.run(Project.java:618)
	at org.eclipse.core.internal.resources.Workspace.run(Workspace.java:2345)
	at org.eclipse.core.internal.resources.Project.internalBuild(Project.java:597)
	at org.eclipse.core.internal.resources.Project.build(Project.java:124)
	at com.android.ide.eclipse.adt.internal.project.ProjectHelper.doFullIncrementalDebugBuild(ProjectHelper.java:1143)
	at com.android.ide.eclipse.adt.internal.launch.LaunchConfigDelegate.launch(LaunchConfigDelegate.java:155)
	at org.eclipse.debug.internal.core.LaunchConfiguration.launch(LaunchConfiguration.java:858)
	at org.eclipse.debug.internal.core.LaunchConfiguration.launch(LaunchConfiguration.java:707)
	at org.eclipse.debug.internal.ui.DebugUIPlugin.buildAndLaunch(DebugUIPlugin.java:1018)
	at org.eclipse.debug.internal.ui.DebugUIPlugin$8.run(DebugUIPlugin.java:1222)
	at org.eclipse.core.internal.jobs.Worker.run(Worker.java:53)
[2014-05-18 02:40:22 - SuperRace-android] Dx 1 error; aborting
[2014-05-18 02:40:22 - SuperRace-android] Conversion to Dalvik format failed with error 1


i have no idea how to solve this and i need to present this project in few hours … help me please !
how to know where are the duplicate libs and how to remove them ?