LINQPad 5.33.7 (Any CPU) - Premium Edition - System.MissingMethodException

When opening linqpad I get the following exception dialog
System.MissingMethodException: Method not found: 'Void Microsoft.CodeAnalysis.CSharp.CSharpCompilationOptions..ctor
Let me know if I can provide more information


  • After downloading the zip, you need to put the files into a clean folder (with no other assemblies or subfolders containing assemblies).
  • The folder contains the following files only
    Directory: C:\Program Files (x86)\LINQPad5                               
    Mode                LastWriteTime         Length Name                        
    ----                -------------         ------ ----                        
    -a----       21/08/2018   3:39 PM       25477264 LINQPad.exe                 
    -a----       21/08/2018   3:39 PM           2430 LINQPad.exe.config          
    -a----       21/08/2018   3:39 PM            400 lprun readme.txt            
    -a----       21/08/2018   3:39 PM          11448 lprun.exe                   
    -a----       21/08/2018   3:39 PM           2463 lprun.exe.config            
    -a----       10/07/2017   1:48 PM         294788 passwords.bin         
    If I overwrite the files with v5.31.00 (AnyCpu) ( I don't get the exception
  • Are there any subfolders in C:\Program Files (x86)\LINQPad?

    Also, could you tell me whether there are any Roslyn assemblies in the GAC:

    And have you enabled the experimental Roslyn assemblies in Edit | Preferences | Query?
  • I just downloaded the beta again, extracted into its own folder, ran and got the same exception
  • 1) No, there are no subfolders in C:\Program Files (x86)\LINQPad
    2) 0 assemblies in the GAC (after running the script)
    3) Experimental Roslyn assemblies are enabled (current version
  • Can you try updating the experimental Roslyn assemblies to And if that doesn't work, does it work if you uncheck the experimental Roslyn assemblies feature?
  • Don't worry, I've got a repro. It seems the Roslyn assemblies use optional parameters in such a way to give consumers forward - but not backward - compatibility.

    To fix it, either upgrade to, or download the new beta (which disables the Roslyn prototype assemblies until you download the newer version).
  • All good now...thanks Joe
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