Error building Player: CommandInvokationFailure: Unable to convert classes into dex format

Please help me to solve this problem. This is what i got in the console:

Error building Player: CommandInvokationFailure: Unable to convert classes into dex format. See the Console for details.

C:\Program Files\Java\jdk1.8.0_25\bin\java.exe -Xmx1024M -Dcom.android.sdkmanager.toolsdir="D:/Android SDK/sdk\tools" -Dfile.encoding=UTF8 -jar "D:/Unity3D/Data/BuildTargetTools/AndroidPlayer\sdktools.jar" -

stderr[

UNEXPECTED TOP-LEVEL EXCEPTION:
java.lang.IllegalArgumentException: already added:       Lcom/google/android/gms/internal/qn;
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:732)
at com.android.dx.command.dexer.Main.processFileBytes(Main.java:673)
at com.android.dx.command.dexer.Main.access$300(Main.java:83)
at com.android.dx.command.dexer.Main$1.processFileBytes(Main.java:602)
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.process(ClassPathOpener.java:144)
at com.android.dx.command.dexer.Main.processOne(Main.java:632)
at com.android.dx.command.dexer.Main.processAllFiles(Main.java:510)
at com.android.dx.command.dexer.Main.runMonoDex(Main.java:280)
at com.android.dx.command.dexer.Main.run(Main.java:246)
at com.android.dx.command.dexer.Main.main(Main.java:215)
at com.android.dx.command.Main.main(Main.java:106)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:483)
at SDKMain.main(SDKMain.java:130)
1 error; aborting
]
stdout[
processing archive bin\classes.jar...
processing com/unity3d/player/a$1.class...
processing

and a million of procesing somethings ... it took 320k line so i wasnt able to paste it here.

This usually happens for the plugins. Search for any duplicate jar in the explorer of your project. Delete any duplicates. If it doesn't solve your problem, try deleting your "Plugins" folder of your project and then re-import all your plugins. Hope it will be solved.