System.Collections.Specialized.OrderedDictionary doesn't exist in target framework while building for windows 8.

I am compiling my game for windows 8 and it always gives me this error

Error building Player: Exception: Error: type System.Collections.Specialized.OrderedDictionary doesn’t exist in target framework.

everything works fine for iOS and android but I am getting this error on windows 8.

is there any solution for this.Please guys help me out.

I;m getting the same error, don;t know what it is…

OrderedDictionary is only used in UIPanel.cs of NGUI and I fixed it by updating my NGUI.Hope this works for you.