Castle.core 5.0.0 upgrade issues

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C#

We have tried to upgrade the Castle.Core NuGet package to version 5.0.0 but we now get errors on the following line in our Container Manager object:
Container = new WindsorContainer();

The error we get is as follows:
$exception {"Could not load type 'Castle.Core.Internal.PermissionUtil' from assembly 'Castle.Core, Version=5.0.0.0, Culture=neutral, PublicKeyToken=407dd0808d44fbdc'.":"Castle.Core.Internal.PermissionUtil"} System.TypeLoadException

THe issue also happens when we try to upgrade Moq which appears to depend on Castle.Core

Is anyone else experiencing this problem and are there any solutions available?

Many thanks

What I have tried:

Googling for a solution on the internet