Interop.Plantronics.dll still gives the ISessionCOMManager missing reference?

Hello,

I am trying to run the SpokesSDKCOMNETSample which says I need to add the Spokes 2.7's dll named Interop.Plantronics, which I am unable to find the downloading link of spokes 2.7 so, I just added the reference of spokes 3.6's Interop.Plantronics.dll and it still giving me the same old error

Any help is appreciated,

Thanks