ArgumentException: The Assembly System.Configuration is referenced by System.Data. But the dll is not allowed to be included or could not be found.

When i want to build and run in google native client , it stopped and this error popped out. I have already set my optimization compatibility level to .net 2.0. Anyone has any idea why and what is wrong? UnityEditor.AssemblyHelper.AddReferencedAssembliesRecurse (System.String assemblyPath, System.Collections.Generic.List`1 alreadyFoundAssemblies, System.String[] allAssemblyPaths, System.String[] foldersToSearch, System.Collections.Generic.Dictionary`2 cache, BuildTarget target) (at C:/BuildAgent/work/d3d49558e4d408f4/Editor/Mono/AssemblyHelper.cs:114) UnityEditor.AssemblyHelper.AddReferencedAssembliesRecurse (System.String assemblyPath, System.Collections.Generic.List`1 alreadyFoundAssemblies, System.String[] allAssemblyPaths, System.String[] foldersToSearch, System.Collections.Generic.Dictionary`2 cache, BuildTarget target) (at C:/BuildAgent/work/d3d49558e4d408f4/Editor/Mono/AssemblyHelper.cs:117) UnityEditor.AssemblyHelper.AddReferencedAssembliesRecurse (System.String assemblyPath, System.Collections.Generic.List`1 alreadyFoundAssemblies, System.String[] allAssemblyPaths, System.String[] foldersToSearch, System.Collections.Generic.Dictionary`2 cache, BuildTarget target) (at C:/BuildAgent/work/d3d49558e4d408f4/Editor/Mono/AssemblyHelper.cs:117) UnityEditor.AssemblyHelper.FindAssembliesReferencedBy (System.String[] paths, System.String[] foldersToSearch, BuildTarget target) (at C:/BuildAgent/work/d3d49558e4d408f4/Editor/Mono/AssemblyHelper.cs:149) UnityEditor.HostView:OnGUI()