Cannot load assembly System.Security.Permissions.dll

Unity version: 2020.3.23f1
Scripting backend: Mono
API compatibility level: .NET 4.x
Platform: Windows Standalone 64

I am trying to use a plugin that depends on Python.Runtime (NuGet Gallery | pythonnet_netstandard_py37_win 2.5.2) version 2.5.2, which targets .NET Standard 2.0.

Since NuGet does not work with Unity, I imported Python.Runtime.dll as follows: Download the .nupkg from the NuGet website, extract it, then import Python.Runtime.dll to Assets/Plugins/x86_64.

I got a compiler error that I was missing System.Security.Permissions.dll, which is a dependency of Python.Runtime. I followed the same procedure described above to get System.Security.Permissions from NuGet (NuGet Gallery | System.Security.Permissions 8.0.0) into my project (there are a few versions of the .dll in the download, I used the .NET Standard 2.0 version). I get the following errors:

Error: Could not load signature of System.Security.HostSecurityManager:smile:etermineApplicationTrust due to: Could not resolve type with token 0100002f (from typeref, class/assembly System.Security.Policy.EvidenceBase, System.Security.AccessControl, Version=6.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a) assembly:System.Security.AccessControl, Version=6.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a type:System.Security.Policy.EvidenceBase member:(null) signature:

Unloading broken assembly Assets/Plugins/x86_64/System.Security.Permissions.dll, this assembly can cause crashes in the runtime

and cannot use the library that depends on System.Security.Permissions (calls to it hang indefinitely).

I also tried using a newer version of System.Security.Permissions.dll and redirecting the assembly versions to avoid a version conflict, but I still got similar errors. This reference Unity - Manual: .NET profile support states that .NET Standard plugins can be used with API compatibility level .NET 4.x, does anyone know why this particular DLL won’t load?

Hi,have you resolved this problem?

Same Problem here…

this stackoverflow answer seemed to solve it for me c# - Conflicting libraries System.Security.Permissions and mscorlib when updating from Unity 2021.3.13f to 2021.3.14f - Stack Overflow