Unable to cast object of type 'System.RuntimeType' to type 'Mono.Debugger.Soft.TypeMirror'. RRS feed

  • Question

  • Visual Studio 2017, version 15.5.2.

    I created a Blank Xamarin Forms, Cross Platform project using .NetStandard option.

    My project was working fine prior to upgrade to this version.  Now a simple List creation is null and when I tried to add an item to the list, it keep getting 

    Unable to cast object of type 'System.RuntimeType' to type 'Mono.Debugger.Soft.TypeMirror'.

    public void Test()
                List<Int32> list= new List<Int32>();
                //Unable to cast object of type 'System.RuntimeType' to type 'Mono.Debugger.Soft.TypeMirror'.

                int x = 0;
                int y = x + 1;

    This error is causing other problems with deserialization of List<T>

    I even installed a VS 2017 on a fresh Windows 7 machine and still get the same issue.

    (I would have added pictures but the site won't let it because it couldn't verify my account yet)

    Tuesday, January 9, 2018 7:54 PM


  • Hi Kag007,

    This forum is discussing Visual Studio WPF/SL Designer, Visual Studio Guidance Automation Toolkit, Developer Documentation and Help System, and Visual Studio Editor.

    Your issue is related to Xamarin, I suggest you repost a new thread to the following forum for a professional answer.


    Or, you could get advice on Stack Overflow and just add a tag with Xamarin in your thread, and then you would get support from Xamarin members.



    MSDN Community Support
    Please remember to click "Mark as Answer" the responses that resolved your issue, and to click "Unmark as Answer" if not. This can be beneficial to other community members reading this thread. If you have any compliments or complaints to MSDN Support, feel free to contact MSDNFSF@microsoft.com.

    • Edited by Judy ZhuY Wednesday, January 10, 2018 7:11 AM
    • Proposed as answer by pituachMVP Thursday, January 11, 2018 6:34 AM
    • Marked as answer by Dave PatrickMVP Tuesday, January 16, 2018 8:18 PM
    Wednesday, January 10, 2018 7:03 AM