Omnisharp-vscode: System.TypeLoadException: Could not load type of field 'McMaster.Extensions.CommandLineUtils.CommandLineApplication:_validationErrorHandler' (36) due to: Could not load file or assembly 'System.ComponentModel.DataAnnotations, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35' or one of its dependencies.

[mfgabriel92]

Issue Description

An error message when OmniSharp initializes on a newly created webapi project.

Steps to Reproduce

Create a webapi project and install OmniSharp

Expected Behavior

To have no error.

Actual Behavior

Error.

Logs

OmniSharp log

Starting OmniSharp server at 1/30/2020, 11:51:34 AM
    Target: /home/gabriel/Workspace/careplus-email-api

OmniSharp server started with Mono 5.18.0.
    Path: /home/gabriel/.vscode/extensions/ms-vscode.csharp-1.21.9/.omnisharp/1.34.9/omnisharp/OmniSharp.exe
    PID: 24986

System.TypeLoadException: Could not load type of field 'McMaster.Extensions.CommandLineUtils.CommandLineApplication:_validationErrorHandler' (36) due to: Could not load file or assembly 'System.ComponentModel.DataAnnotations, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35' or one of its dependencies.
  at OmniSharp.Stdio.StdioCommandLineApplication..ctor () [0x00000] in <27dcabbd1f5d4edeaffe820a1236c676>:0 
  at OmniSharp.Stdio.Driver.Program+<>c__DisplayClass0_0.<Main>b__0 () [0x00006] in <2d02054c9f224f8aa95299738e820ffb>:0 
  at OmniSharp.HostHelpers.Start (System.Func`1[TResult] action) [0x0001c] in <1ed0cdfb5a5d42889b4f5df087ff7bd6>:0 
[ERROR] Error: OmniSharp server load timed out. Use the 'omnisharp.projectLoadTimeout' setting to override the default delay (one minute).

C# log

I don't know how to do it

Environment information

VSCode version: 1.41.1
C# Extension: 1.21.9
OS: Ubuntu 19.10 64 bits

Mono Information

OmniSharp using global mono :5.18.0

Dotnet Information

.NET Core SDK (reflecting any global.json):
Version: 3.1.101
Commit: b377529961

Runtime Environment:
OS Name: ubuntu
OS Version: 19.10
OS Platform: Linux
RID: ubuntu.19.10-x64
Base Path: /usr/share/dotnet/sdk/3.1.101/

Host (useful for support):
Version: 3.1.1
Commit: a1388f194c

.NET Core SDKs installed:
3.1.101 [/usr/share/dotnet/sdk]

.NET Core runtimes installed:
Microsoft.AspNetCore.App 3.1.1 [/usr/share/dotnet/shared/Microsoft.AspNetCore.App]
Microsoft.NETCore.App 3.1.1 [/usr/share/dotnet/shared/Microsoft.NETCore.App]

To install additional .NET Core runtimes or SDKs:
https://aka.ms/dotnet-download

Visual Studio Code Extensions

|Extension|Author|Version|
|---|---|---|
|csharp|ms-vscode|1.21.9|
|dart-code|Dart-Code|3.7.1|
|flutter|Dart-Code|3.7.1|
|vscode-great-icons|emmanuelbeziat|2.1.47|;

[JoeRobich]

OmniSharp server started with Mono 5.18.0.

Hi @mfgabriel92, OmniSharp requires Mono 6.6.0 or higher. Can you update to the stable release? https://www.mono-project.com/download/stable/#download-mac

[mfgabriel92]

Hi @JoeRobich. It solved it. Thanks.

[mfgabriel92]

Hello,

It happened again, and this time I have version 6.8.0.105.

[jpietrzyk]

Have the same problem, maybe the reason is I've just updated to Ubuntu 20.04 beta, and yeah, it is beta, but will be stable in 10 days. My output:

System.TypeLoadException: Could not load type of field 'McMaster.Extensions.CommandLineUtils.CommandLineApplication:_validationErrorHandler' (36) due to: Could not load file or assembly 'System.ComponentModel.DataAnnotations, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35' or one of its dependencies.
  at OmniSharp.Stdio.StdioCommandLineApplication..ctor () [0x00000] in <0f4d64c713a44cb7b327f623e35918a5>:0 
  at OmniSharp.Stdio.Driver.Program+<>c__DisplayClass0_0.<Main>b__0 () [0x00006] in <053e8164eb434b63be8247033b33692f>:0 
  at OmniSharp.HostHelpers.Start (System.Func`1[TResult] action) [0x0001c] in <cc784888e5004669a7cdfce6a3d2dba5>:0 
[ERROR] Error: OmniSharp server load timed out. Use the 'omnisharp.projectLoadTimeout' setting to override the default delay (one minute).

[konradmb]

@jpietrzyk Basically, OmniSharp can't load required assemblies. You can try either installing mono-complete package or setting "omnisharp.useGlobalMono": "never" in VSCode settings.

Installing mono-complete is a better way, because you'll get more libraries, newer version etc.

I wonder why loading internal mono isn't the default, especially when OmniSharps ships it inside the extension, and Ubuntu has a stripped down version of mono by default.
But it could lead to even more problems…

[Semicolon192]

@konradmb Yes! sudo apt install mono-complete fixed it for me. Pop!_os 20.04 mono 6.8.0.105