System.PlatformNotSupportedException when making calls from iPhone client - visual-studio

Question

I'm trying to have Tasks working under Visual Studio 2012 with MonoTouch. I'm using ALPHA channel and have the latest releases installed.
There are 3 projects in solution:
1. PCL (158 target platforms) with async methods
2. Touch
3. Android
This code compiles, could be deployed and executed. But when I make calls from iPhone client:
var asyncResult = await MyClass.DoStuff();
Console.WriteLine("doing stuff completed: " + asyncResult);
I get the following result:
System.PlatformNotSupportedException: This platform is not supported
at await part of code. When I write it with Task.ContinueWith - same result.
What is interesting is doesn't work only under Visual Studio + MonoTouch. All other configurations launches this code correctly (WIN+VS+Android, WIN+VS+Android, MAC+XS+iOS, MAC+XS+Android)
Versions of SDK are synchronized with the latest ALPHA release.
Exception details:
Unhandled Exception:
System.PlatformNotSupportedException: This platform is not supported.
2013-07-25 11:45:32.384 iPhone[1817:907] Unhandled managed exception: This platform is not supported. (System.PlatformNotSupportedException)
at System.ExecutionContextLightup.Run (System.ExecutionContextLightup executionContext, System.Action`1 callback, System.Object state) [0x00000] in <filename unknown>:0
at System.Runtime.CompilerServices.AsyncMethodBuilderCore+MoveNextRunner.Run () [0x00000] in <filename unknown>:0
at Microsoft.Runtime.CompilerServices.TaskAwaiter+<>c__DisplayClassa.<OnCompletedInternal>b__1 (System.Object state) [0x00000] in <filename unknown>:0
at MonoTouch.UIKit.UIKitSynchronizationContext+<Post>c__AnonStorey52.<>m__4E () [0x00000] in /Developer/MonoTouch/Source/monotouch/src/UIKit/UIKitSynchronizationContext.cs:24
at MonoTouch.Foundation.NSAsyncActionDispatcher.Apply () [0x00000] in /Developer/MonoTouch/Source/monotouch/src/shared/Foundation/NSAction.cs:87
at (wrapper managed-to-native) MonoTouch.UIKit.UIApplication:UIApplicationMain (int,string[],intptr,intptr)
at
MonoTouch.UIKit.UIApplication.Main (System.String[] args, System.String principalClassName, System.String delegateClassName) [0x0004c] in /Developer/MonoTouch/Source/monotouch/src/UIKit/UIApplication.cs:38
at iPhone.Application.Main (System.String[] args) [0x00001] in c:\Sources\Local\PCL_XN\iPhone\Main.cs:17
The program 'Mono' has exited with code 0 (0x0).
The program '[6760] iPhone.vshost.exe: Managed (v4.0.30319)' has exited with code -1 (0xffffffff).

Answer 1

A bit of a late reply, but in case anyone is still running into this, it looks like one workaround is to add --nolinkaway --linkskip=mscorlib under "Project Options -> iOS Build -> Additional mtouch arguments" for the main application project.
Without this, the linker removes something from mscorlib that the Microsoft.Bcl package requires for its compatibility checks.
Bug filed here: https://bugzilla.xamarin.com/show_bug.cgi?id=15290