I have the following code in a tester class in my main assembly, PocoGenerator. This assembly is supposed to use a T4 template to generate POCO\'s based on L2S
I had a similar problem when I tried to include Less Css for .NET in my Web project.
I've ended up with copying the assembly in the root folder of my project and including it as a reference in the project itself. Then, I've added the following lines in the .tt file:
<#@ assembly name="dotless.Core.dll" #>
<#@ import namespace="dotless.Core" #>
<#@ import namespace="dotless.Core.configuration" #>
I'm sure that something similar should work with your assembly as well...