以前，我能够使用Unity 4.6.2构建iOS项目，但我不能使用Unity 5.1.1。我找不到iGUI dll错误：
ArgumentException: The Assembly UnityEditor is referenced by iGUI ('Assets/lib/igui/Runtime/iGUI.dll'). But the dll is not allowed to be included or could not be found.
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 /Users/builduser/buildslave/unity/build/Editor/Mono/AssemblyHelper.cs:154)
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 /Users/builduser/buildslave/unity/build/Editor/Mono/AssemblyHelper.cs:160)
UnityEditor.AssemblyHelper.FindAssembliesReferencedBy (System.String[] paths, System.String[] foldersToSearch, BuildTarget target) (at /Users/builduser/buildslave/unity/build/Editor/Mono/AssemblyHelper.cs:192)
UnityEditor.HostView:OnGUI()
可能是什么问题？