I am migrating from BizTalk 2013 to R2 and in doing so the BizTalk Development Framework missed the assembly Microsoft.BizTalk.Interop.SSOClient from version 5.0.1.0. I could see that newer versions were installed in the .net 4.0 GAC.
So if you run into the same problem, you could download the BizTalk Development Framework sourcode and could manually put the missing assembly into the .net 2.0 GAC
