Custom Action in C# used via WiX fails with error 1154

It sounds like you are using DTF. If you see:

using Microsoft.Deployment.WindowsInstaller;

then you certainly are. Be sure to read the following for how it all works:

Deployment Tools Foundation (DTF) Managed Custom Actions

Also you'll find a DTF help chm in the start menu under WiX.

Basically it sounds like to me you are wiring the .NET assembly into the installer instead of the unmanged wrapper dll. Read the above article for an overview of how to look at it in Depends and to know what to expect. The WiX | C# Custom Action project should output Foo.dll and Foo.CA.dll. You want the later in your installer.

For people who land on this page in the future (the answer was originally for the poster ) there is a whole list of things to check:

1. Are you referencing the correct DLL in the Binary table?
2. Are you referencing the correct exported function name?
3. Is your class public?
4. Is your method using the correct signature? I.e. is it:
5. Marked with the correct CustomAction attribute
6. Marked as public?
7. Marked as static?
8. Return ActionResult?
9. Take Session as an Argument?
10. Make sure you are using the WiX C# Custom Action Project type to ensure the postbuild event is called to create the native DLL wrapper. (See #1)

Any one of these can cause an 1154 error. This is the reason I wrote a comprehensive blog article on the subject and linked to it in this answer. It's important to fully understand how managed code is presented to the unmanaged Windows Installer service and to know how to use Depends to validate that the public static method is exported as a stdcall function in the resulting .CA.dll that WiX/DTF produces.

If you create your custom action in Visual Studio (Votive) be sure that you created a Wix Custon Action project and not a class library, otherwise you have to use MakeSfxCA tool to pack your custom action.

I just found the same issue (using the correct .CA.dll file) and in my case it was because I wasn't using a static method. I had this:

public ActionResult MyMethod(Session session)

Instead of this:

public static ActionResult MyMethod(Session session)

After changing the method it worked just fine.

Hope it helps someone.