EnvDTE not found in VS2012 works in VS2010

Question

I'm using EnvDTE to do some code generation within my T4 Templates.

I have the code working correctly in Visual Studio 2010, however I've just started using Visual Studio 2012 and now when I try to run my templates I get the following error

Compiling transformation: Metadata file 'EnvDTE.dll' could not be found 

I don't actually have a reference to EnvDTE in my project as its a Silverlight class library and I wasn't able to add the DLL, however it finds the DLL somehow.

I'm not sure what is difference is between 10 and 12 to cause this.

The following are my imports and assembly definitions from the start of my ttinclude file.

<#@ template debug="true" hostSpecific="true" #>
<#@ output extension=".generated.cs" #>
<#@ Assembly Name="EnvDTE.dll" #>
<#@ Assembly Name="System.Data" #>
<#@ import namespace="EnvDTE" #>
<#@ import namespace="System.Data" #>
<#@ import namespace="System.Data.SqlClient" #>
<#@ import namespace="System.IO" #>
<#@ import namespace="System.Text.RegularExpressions" #>

Is there anything I have to do differently to get it working for Visual Studio 2012