using Array.Sort Method (Array, Array) in a Metro App

I've been using the two array sort method in my Unity app for iOS & Android. I'm now moving it to Windows 8 Store - which is a far from trivial process, so many things just don't work...

Anyway, I can't get the app to compile with the following code:

int[] btCopy = (int[])SpawnGamePieces.Instance.bubbleTypeCount.Clone(); System.Array.Sort(btCopy,indexes);

indexes is a int[] array that has been declared earlier - the idea here is to sort the index based on the order of the values in btCopy.

Anyway, it works exactly as is and as I want on iOS/Android - but on Metro I get the following compile error:

Argument 2: cannot convert from 'int[]' to 'System.Collections.IComparer'

Obviously it's not recognizing the (Array,Array) method - does it just not exist in the Metro port? Other than writing my own function, any way around this?