Can’t seem to compile my project in 4.16. I’m using the Release branch but packaged into a binary build. Never seen this issue before… tried regenerating. clearing cached files etc. No luck 
Default 4.17 project compiles fine.
1>------ Build started: Project: UE4, Configuration: BuiltWithUnrealBuildTool Win32 ------
2>------ Build started: Project: ECGame, Configuration: Development_Editor x64 ------
2> Creating makefile for ECGameEditor (no existing makefile)
2> Performing full C++ include scan (no include cache file)
2>EXEC : error : System.ArgumentException: An item with the same key has already been added.
2> at System.ThrowHelper.ThrowArgumentException(ExceptionResource resource)
2> at System.Collections.Generic.Dictionary`2.Insert(TKey key, TValue value, Boolean add)
2> at UnrealBuildTool.UEBuildTarget.Build(BuildConfiguration BuildConfiguration, CPPHeaders Headers, List`1 OutputItems, List`1 UObjectModules, ActionGraph ActionGraph)
2> at UnrealBuildTool.UnrealBuildTool.RunUBT(BuildConfiguration BuildConfiguration, String] Arguments, FileReference ProjectFile)
2>C:\Program Files (x86)\MSBuild\Microsoft.Cpp\v4.0\V140\Microsoft.MakeFile.Targets(41,5): error MSB3075: The command "C:\UE4_Builds\UE4_Eclipse\Engine\Build\BatchFiles\Build.bat ECGameEditor Win64 Development "E:\P4\JBaxter_Work\Eclipse\Eclipse_Steam\ECGame\ECGame.uproject" -waitmutex" exited with code 5. Please verify that you have sufficient rights to run this command.
========== Build: 1 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========
Answerhub: https://answers.unrealengine.com/questions/666969/cant-compile-in-417.html