Why doesn't NAnt generate a bootstrapper file after calling MSBuild on a project?

I have a project with this in its MSBuild script:

  <Target Name="AfterBuild">
    <GenerateBootstrapper ApplicationFile="MyApp.msi" ApplicationName="My App" BootstrapperItems="@(BootstrapperFile)" OutputPath="$(OutputPath)" Culture="en-US" CopyComponents="true" ComponentsLocation="HomeSite" Path="C:\Program Files (x86)\Microsoft SDKs\Windows\v7.0A\Bootstrapper" />
  </Target>

If I run the project in visual studio, that gets run after the build and a setup.exe bootstrapper file is created in my bin/debug directory. However, if I build that same project (a WiX project, if that matters) under NAnt, everything gets built in the output directory that NAnt specifies, except the bootstrapper file. Nothing is being buil开发者_高级运维t in the project's bin/debug directory when I build it under NAnt, so the setup.exe file doesn't seem to be getting built, even there. I don't think that the AfterBuild step is even being run.

How can I generate this bootstrapper file under NAnt?

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I had to specify the variable OutputPath in my NAnt script: