I am trying to create a WiX custom action which will allow me to shutdown and clear down a COM+ package as part of an upgrade installation, or create and configure a new COM+ package as part of the initial installation. I previously had this running as a CustomAction within a standard Visual Studio MSI but this only allows the custom action to be executed after the files have been copied - which will fail as the package will still be running. The COMAdmin.dll has been added as a reference to the CustomAction project and is set CopyLocal=true. In the bin folder for the custom action project the Interop.COMAdmin.dll is present. The answer to this question seems to suggest that it should work. I am getting the following exception within the MSI log when trying to install: MSI (s) (C4:04) [10:40:34:205]: Invoking remote custom action. DLL: C:\WINDOWS\Installer\MSI119.tmp, Entrypoint: BeforeInstall SFXCA: Extracting custom action to temporary directory: C:\WINDOWS\Installer\MSI119.tmp-\ SFXCA: Binding to CLR version v2.0.50727 Calling custom action MyCustomAction!MyCustomAction.CustomActions.BeforeInstall Exception thrown by custom action: System.Reflection.TargetInvocationException: Exception has been thrown by the target of an invocation. ---> System.IO.FileNotFoundException: Could not load file or assembly 'Interop.COMAdmin, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null' or one of its dependencies. The system cannot find the file specified. File name: 'Interop.COMAdmin, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null' at MyCustomAction.CustomActions.BeforeInstall(Session session) WRN: Assembly binding logging is turned OFF. To enable assembly bind failure logging, set the registry value (DWORD) to 1. Note: There is some performance penalty associated with assembly bind failure logging. To turn this feature off, remove the registry value . --- End of inner exception stack trace --- at System.RuntimeMethodHandle._InvokeMethodFast(Object target, Object arguments, SignatureStruct& sig, MethodAttributes methodAttributes, RuntimeTypeHandle typeOwner) at System.RuntimeMethodHandle.InvokeMethodFast(Object target, Object arguments, Signature sig, MethodAttributes methodAttributes, RuntimeTypeHandle typeOwner) at System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder, Object parameters, CultureInfo culture, Boolean skipVisibilityChecks) at System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder, Object parameters, CultureInfo culture) at Microsoft.Deployment.WindowsInstaller.CustomActionProxy.InvokeCustomAction(Int32 sessionHandle, String entryPoint, IntPtr remotingDelegatePtr)