Microsoft.Tools.WindowsInstallerXml.AssemblyDefaultWixExtensionAttribute' was not defined

[fng2]

This has probably come up before but despite my googling and searching here I could not find an answer.
I am building an excel VSTO addin using VS2015 and Wix 3.11. Same setup I've used several times. After adding the default Wix setup project and building the solution I get the above error. In the Wix project I have added references to the the addin dll (which builds fine), the wixUIExtension, the wixUtilExtension and product.wxs. These are the same steps I have used before without issue so I am not sure why wix is not able to use any of it's built in variables. It is probably something simple, but eluding me now.
here is my product.wxs:
`

	<MajorUpgrade DowngradeErrorMessage="A newer version of [ProductName] is already installed." />
<MediaTemplate EmbedCab="yes" />
<UIRef Id="WixUI_Mondo" />
<!-- override default license -->
<WixVariable Id="WixUILicenseRtf" Value="License.rtf" />

	<Feature Id="ProductFeature" Title="HIRFSetup" Level="1">
		<ComponentGroupRef Id="ProductComponents" />
	</Feature>
</Product>

<Fragment>
	<Directory Id="TARGETDIR" Name="SourceDir">
		<Directory Id="ProgramFilesFolder">
			<Directory Id="INSTALLFOLDER" Name="HIRFSetup" />
		</Directory>
	</Directory>
</Fragment>

<Fragment>
	<ComponentGroup Id="ProductComponents" Directory="INSTALLFOLDER">
		<!-- TODO: Remove the comments around this Component element and the ComponentRef below in order to add resources to this installer. -->
		<!-- <Component Id="ProductComponent"> -->
			<!-- TODO: Insert files, registry keys, and other resources here. -->
		<!-- </Component> -->

  <!-- VSTO framework file -->
  <Component>
    <File Source="$(var.HIRFAddin.TargetDir)Microsoft.Office.Tools.Common.v4.0.Utilities.dll"></File>
  </Component>

</ComponentGroup>
</Fragment>

`

Thanks for any pointers !

[barnson]

added references to the the addin dll

Don't do that. References are WiX extension DLLs.

[fng2]

I misspoke, I did not add a reference to the addin.dll, it was a reference to the addin project. This is how it is on all my other projects which work fine and removing it does not help. Wix is still unaware of it's built in variables.

[barnson]

The error message says you have a reference to a DLL that isn't a WiX extension. Check the .wixproj.

[fng2]

Ok, I found the problem. My addin was named "HIRFAddin" or so I thought. When I created the project in VS I miss typed "HIRFAddIn". Note the capitol "I" in addin. My references were defined as using "HIRFAddin" and Wix being very case sensitive was not registering them. Once I fixed that all was well.
Thanks