Error:Execution failed for task ':app:transformDexArchiveWithExternalLibsDexMergerForDebug'.

Error:Execution failed for task ':app:transformDexArchiveWithExternalLibsDexMergerForDebug'.
> java.lang.RuntimeException: java.lang.RuntimeException: com.android.builder.dexing.DexArchiveMergerException: Unable to merge dex

android {

...

defaultConfig {

 ...

 multiDexEnabled true

} 

}