ios stripping build errors

When building for iOS on mac using Unity 5..5.2f1 i get stripping errors below, if i set scripting backend to Mono2x the error goes away, ,any ideas what is the problem?

 Failed running /Applications/Unity/Unity.app/Contents/Tools/UnusedByteCodeStripper2/UnusedBytecodeStripper2.exe --api NET_2_0_Subset -out "/Users/da/Desktop/Unity/picnmix/Temp/StagingArea/Data/Managed/tempStrip" -l none -c link -b False -x "/Applications/Unity/PlaybackEngines/iOSSupport/Whitelists/Core.xml" -f "/Applications/Unity/Unity.app/Contents/il2cpp/LinkerDescriptors" -x "/Users/da/Desktop/Unity/picnmix/Temp/StagingArea/Data/Managed/../platform_native_link.xml" -x "/Users/da/Desktop/Unity/picnmix/Temp/StagingArea/Data/methods_pointedto_by_uievents.xml" -x "/Users/da/Desktop/Unity/picnmix/Temp/StagingArea/Data/preserved_derived_types.xml" -x "/Users/da/Desktop/Unity/picnmix/Assets/link.xml" -d "/Users/da/Desktop/Unity/picnmix/Temp/StagingArea/Data/Managed" -a  "/Users/da/Desktop/Unity/picnmix/Temp/StagingArea/Data/Managed/Assembly-CSharp-firstpass.dll" -a  "/Users/da/Desktop/Unity/picnmix/Temp/StagingArea/Data/Managed/Assembly-CSharp.dll" -a  "/Users/da/Desktop/Unity/picnmix/Temp/StagingArea/Data/Managed/UnityEngine.UI.dll" -a  "/Users/da/Desktop/Unity/picnmix/Temp/StagingArea/Data/Managed/UnityEngine.Analytics.dll" -a  "/Users/da/Desktop/Unity/picnmix/Temp/StagingArea/Data/Managed/TextMeshPro.dll"
     
     stdout:
     Fatal error in Mono CIL Linker
     System.IO.FileNotFoundException: Could not find file "/Applications/Unity/PlaybackEngines/iOSSupport/Whitelists/Core.xml".
     File name: '/Applications/Unity/PlaybackEngines/iOSSupport/Whitelists/Core.xml'
       at System.IO.FileStream..ctor (System.String path, FileMode mode, FileAccess access, FileShare share, Int32 bufferSize, Boolean anonymous, FileOptions options) <0x105673120 + 0x007f0> in <filename unknown>:0 
       at System.IO.FileStream..ctor (System.String path, FileMode mode, FileAccess access, FileShare share, Int32 bufferSize) <0x1056730b0 + 0x00055> in <filename unknown>:0 
       at (wrapper remoting-invoke-with-check) System.IO.FileStream:.ctor (string,System.IO.FileMode,System.IO.FileAccess,System.IO.FileShare,int)
       at System.Xml.XmlDownloadManager.GetStream (System.Uri uri, ICredentials credentials, IWebProxy proxy, System.Net.Cache.RequestCachePolicy cachePolicy) <0x105672830 + 0x000b9> in <filename unknown>:0 
       at System.Xml.XmlUrlResolver.GetEntity (System.Uri absoluteUri, System.String role, System.Type ofObjectToReturn) <0x1056725f0 + 0x00095> in <filename unknown>:0 
       at System.Xml.XmlTextReaderImpl.OpenUrlDelegate (System.Object xmlResolver) <0x105672420 + 0x00068> in <filename unknown>:0 
       at System.Xml.XmlTextReaderImpl.OpenUrl () <0x1056720e0 + 0x00139> in <filename unknown>:0 
     stderr:
     
     UnityEngine.Debug:LogError(Object)
     UnityEditorInternal.Runner:RunManagedProgram(String, String, String, CompilerOutputParserBase, Action`1) (at /Users/builduser/buildslave/unity/build/Editor/Mono/BuildPipeline/BuildUtils.cs:96)
     UnityEditorInternal.AssemblyStripper:RunAssemblyLinker(IEnumerable`1, String&, String&, String, String) (at /Users/builduser/buildslave/unity/build/Editor/Mono/BuildPipeline/AssemblyStripper.cs:104)
     UnityEditorInternal.AssemblyStripper:StripAssembliesTo(String[], String[], String, String, String&, String&, String, IIl2CppPlatformProvider, IEnumerable`1) (at /Users/builduser/buildslave/unity/build/Editor/Mono/BuildPipeline/AssemblyStripper.cs:97)
     UnityEditorInternal.AssemblyStripper:RunAssemblyStripper(String, IEnumerable, String, String[], String[], String, IIl2CppPlatformProvider, RuntimeClassRegistry) (at /Users/builduser/buildslave/unity/build/Editor/Mono/BuildPipeline/AssemblyStripper.cs:196)
     UnityEditorInternal.AssemblyStripper:StripAssemblies(String, IIl2CppPlatformProvider, RuntimeClassRegistry) (at /Users/builduser/buildslave/unity/build/Editor/Mono/BuildPipeline/AssemblyStripper.cs:128)
     UnityEditorInternal.IL2CPPBuilder:Run() (at /Users/builduser/buildslave/unity/build/Editor/Mono/BuildPipeline/Il2Cpp/IL2CPPUtils.cs:123)
     UnityEditorInternal.IL2CPPUtils:RunIl2Cpp(String, String, IIl2CppPlatformProvider, Action`1, RuntimeClassRegistry, Boolean) (at /Users/builduser/buildslave/unity/build/Editor/Mono/BuildPipeline/Il2Cpp/IL2CPPUtils.cs:32)
     UnityEditor.HostView:OnGUI()