CannotUnloadAppDomainException is thrown when there is an attempt to unload the following:

• The default application domain, which must remain loaded during the lifetime of the application.

• An application domain with a running thread that cannot immediately stop execution.

• An application domain that has already been unloaded.

CannotUnloadAppDomainException uses the HRESULT COR_E_CANNOTUNLOADAPPDOMAIN, which has the value 0x80131015.

For a list of initial property values for an instance of CannotUnloadAppDomainException, see the CannotUnloadAppDomainException.#ctor constructors.

The following example demonstrates an error that causes the CannotUnloadAppDomainException exception to be thrown.

using System;
using System.Threading;

public class CannotUnloadAppDomainExceptionTest {
  public static void Main() {
    AppDomain ad = Thread.GetDomain();
    AppDomain.Unload(ad);
  }
}

The output is

Unhandled Exception: System.CannotUnloadAppDomainException: The default domain cannot be unloaded.
   at System.AppDomain.Unload(AppDomain domain)
   at CannotUnloadAppDomainExceptionTest.Main()