My client had a preview of the MSMQ/C adapter and was using it in their development environment. When the new MSMQ adapter came out they installed that and promptly received the following error:
The Messaging Engine failed to create the receive adapter "MSMQ". Reason: "Could not load type Microsoft.BizTalk.MsmqAdapter.MsmqReceiver, Microsoft.BizTalk.Adapter.MSMQ.MsmqAdapter,
We were able to fix the problem by following the steps below
After following these steps we did the MSMQ adapter install and all is working.