Unity3d iOS il2cpp Mono.Cecil.AssemblyResolutionException Failed to resolve assembly System.Threading

Unity3d 4.6.7p2 iOS il2cpp Universal .NET Stripping Disabled We've got the error when building our iOS build.
The strange thing is that this error appeared at some point of time on all computers in our office, and if we switch to commits in Git that were built without problems, the error exists.
So we think this error are not related to our changes. We tried to switch to older commits, restart Unity, clean Library folder nothing changes. What can cause such error?

Failed running   /Applications/Unity/Unity.app/Contents/Frameworks/Tools/UnusedByteCodeStripper2/UnusedBytecodeStripper2.exe -out "/PATH/Temp/StagingArea/Data/Managed" -l none -c link -x "/Applications/Unity/Unity.app/Contents/Frameworks/Tools/UnusedByteCodeStripper/native_link.xml" -f "/Applications/Unity/Unity.app/Contents/Frameworks/il2cpp/LinkerDescriptors" -x "/PATH/Temp/StagingArea/Data/Managed/../platform_native_link.xml" -x "/PATH/Temp/StagingArea/Data/methods_pointedto_by_uievents.xml" -x "/PATH/Assets/link.xml" -d "/PATH/Temp/StagingArea/Data/Managed" -a  "/PATH/Temp/StagingArea/Data/Managed/Assembly-CSharp-firstpass.dll" -a  "/PATH/Temp/StagingArea/Data/Managed/Assembly-CSharp.dll" -a  "/PATH/Temp/StagingArea/Data/Managed/Assembly-UnityScript-firstpass.dll" -a  "/PATH/Temp/StagingArea/Data/Managed/Assembly-UnityScript.dll" -a  "/PATH/Temp/StagingArea/Data/Managed/UnityEngine.UI.dll" -a  "/PATH/Temp/StagingArea/Data/Managed/IFacebook.dll" -a  "/PATH/Temp/StagingArea/Data/Managed/Glow11.dll" -a  "/PATH/Temp/StagingArea/Data/Managed/HOTweenMicro.dll" -a  "/PATH/Temp/StagingArea/Data/Managed/ArabicSupport.dll" -a  "/PATH/Temp/StagingArea/Data/Managed/DecalSystem.Runtime.dll" -a  "/PATH/Temp/StagingArea/Data/Managed/P31RestKit.dll" -a  "/PATH/Temp/StagingArea/Data/Managed/P31WinPhoneFlurry.dll" -a  "/PATH/Temp/StagingArea/Data/Managed/P31WinPhoneSocialNetworking.dll" -a  "/PATH/Temp/StagingArea/Data/Managed/P31WinPhoneStore.dll" -a  "/PATH/Temp/StagingArea/Data/Managed/Photon3Unity3D.dll" -a  "/PATH/Temp/StagingArea/Data/Managed/OUR_COMPANY.Phone.dll" -a  "/PATH/Temp/StagingArea/Data/Managed/TPL.dll" -a  "/PATH/Temp/StagingArea/Data/Managed/websocket-sharp.dll"

stdout;
Fatal error in Mono CIL Linker
Mono.Cecil.AssemblyResolutionException: Failed to resolve assembly: 'System.Threading, Version=1.0.2856.102, Culture=neutral, PublicKeyToken=31bf3856ad364e35'
  at Mono.Linker.LinkContext.Resolve (IMetadataScope scope) [0x00000] in <filename unknown>:0 
  at Mono.Linker.Steps.ResolveFromXmlStep.ProcessReferences (Mono.Cecil.AssemblyDefinition assembly, Mono.Linker.LinkContext context) [0x00000] in <filename unknown>:0 
  at Mono.Linker.Steps.ResolveFromXmlStep.GetAssembly (Mono.Linker.LinkContext context, System.String assemblyName) [0x00000] in <filename unknown>:0 
  at Mono.Linker.Steps.ResolveFromXmlStep.ProcessAssemblies (Mono.Linker.LinkContext context, System.Xml.XPath.XPathNodeIterator iterator) [0x00000] in <filename unknown>:0 
  at Mono.Linker.Steps.ResolveFromXmlStep.Process () [0x00000] in <filename unknown>:0 
  at Mono.Linker.Steps.BaseStep.Process (Mono.Linker.LinkContext context) [0x00000] in <filename unknown>:0 
  at Mono.Linker.Pipeline.Process (Mono.Linker.LinkContext context) [0x00000] in <filename unknown>:0 
  at Mono.Linker.Driver.Run () [0x00000] in <filename unknown>:0 
  at Mono.Linker.Driver.RunDriver (Mono.Linker.Driver driver) [0x00000] in <filename unknown>:0 
stderr:

UnityEngine.Debug:LogError(Object)
UnityEditorInternal.Runner:RunManagedProgram(String, String, String, CompilerOutputParserBase)
UnityEditorInternal.AssemblyStripper:RunAssemblyLinker(IEnumerable`1, String&, String&, String, String)
UnityEditorInternal.AssemblyStripper:StripAssembliesTo(String, String, String&, String&, String, String, IEnumerable`1)
UnityEditorInternal.AssemblyStripper:Strip(String, String, String&, String&, String, String, IEnumerable`1)
UnityEditorInternal.AssemblyStripper:Strip(String[], String[], String, String, String&, String&, String, String, IEnumerable`1)
UnityEditorInternal.IL2CPPBuilder:RunAssemblyStripper(IEnumerable, String, String[], String[], String)
UnityEditorInternal.IL2CPPBuilder:StripAssemblies(IEnumerable`1, String)
UnityEditorInternal.IL2CPPBuilder:Run()
UnityEditorInternal.IL2CPPUtils:RunIl2Cpp(String, String, IIl2CppPlatformProvider, Action`1, RuntimeClassRegistry)
UnityEditor.HostView:OnGUI()

link.xml:

<linker>
<assembly fullname="mscorlib">
    <namespace fullname="System.Security.Cryptography" preseve="all"/>
</assembly>

Solution

My colleague solved this by replacing functional from TPL.dll with Parse library, and by removing TPL.dll from project.